By Frederik Pleitgen and Tom Cohen
(CNN)- President Barack Obama said Friday that he has not made a decision on how to respond to the chemical weapons attack in Syria, but he called it "a challenge to the world." President Obama said that the U.S. military and his security team were looking at a "wide range of options" on how to respond to the chemical weapons attack in Syria, but he added that any U.S. action would not involve sending troops or waging a long-term campaign.
A preliminary U.S. government assessment of last week's chemical weapons attack in Syria has made these key findings:
--100 videos attributed to a suspected chemical weapons attack in Syria "show large numbers of bodies exhibiting physical signs consistent with, but not unique to, nerve agent exposure." Some videos show what appear to be fatalities "with no visible injuries" -- imagery "consistent with death from chemical weapons, and inconsistent with death from small-arms, high-explosive munitions or blister agents," said the report, released Friday.
--1,429 people were killed in an August 21 chemical weapons attack in Syria and asserted that "we assess with high confidence that the Syrian government carried out the chemical weapons attack against opposition elements in the Damascus suburbs."
-- The United States says it has "intelligence that leads us to assess that Syrian chemical weapons personnel ... were preparing chemical weapons munitions prior to" what Washington believes was a chemical weapons attack in the Damascus suburbs on August 21. "In the three days prior to the attack, we collected streams of human, signals and geospatial intelligence that reveal regime activities that we assess were associated with preparations for a chemical weapons attack," the U.S. government said in its assessment released Friday.
Citing support from the Arab League, Turkey and France, Secretary of State John Kerry said Friday that "we are not alone in our will to do something about" last week's chemical weapons attack in Syria that he blamed on the regime of President Bashar al-Assad.
Kerry added that the United States "makes our own decisions on our own timelines, based on our own values and interests" in signaling a possible military response to last week's chemical weapons attack in Syria.
[Breaking news alert 1:08 p.m. ET]
A preliminary U.S. government assessment determined that 1,429 people were killed in an August 21 chemical weapons attack in Syria and asserted that "we assess with high confidence that the Syrian government carried out the chemical weapons attack against opposition elements in the Damascus suburbs."
Secretary of State John Kerry said Friday that the American intelligence community has "high confidence" in what he called evidence and facts that the Syrian regime used chemical weapons, adding that "the questions is what are we ... in the world going to do about it."
[Breaking news alert 1:06 p.m. ET]
Secretary of State John Kerry said Friday that Syrian officials made preparations for chemical weapons use for three days prior to the August 21 attack, and that rockets were launched from areas controlled by the Syrian regime and landed in areas controlled by the opposition or contested.
[Breaking news alert 1:04 p.m. ET]
Secretary of State John Kerry said Friday the United States "will not repeat" justifying a military campaign on false intelligence, referring to the Iraq war under President George W. Bush, in detailing information about the chemical weapons attack in Syria.
[Breaking news alert 12:56 p.m. ET]
The U.N. mission inspecting a suspected chemical weapons attack in Syria has completed its collection of samples, said Martin Nesirky, spokesman for the U.N. secretary-general said Friday. Nesirky told reporters that inspectors visited a government military hospital in Damascus and will be leaving Syria on Saturday.
[Breaking news alert 12:40 p.m. ET]
The U.N. mission inspecting a suspected chemical weapons attack in Syria has been completed its collection of samples, said Martin Nesirky, spokesman for the U.N. secretary-general said Friday. Nesirky told reporters that inspectors visited a government military hospital in Damascus and will be leaving Syria on Saturday.
[Breaking news alert 12:22 p.m. ET]
Evidence of another deadly chemical weapons attack in Syria has surfaced, opposition activists said Friday. Seven people died and dozens were injured Monday in the attack on a school in northern Syria.
[Previously published story]
U.N. inspectors began leaving Syria on Friday as U.S. President Barack Obama met with his national security team ahead of the expected release of an intelligence report that blames Syria's government for last week's chemical weapons attack.
The coinciding developments came amid continuing U.S. signals of a possible military attack on Syria in response to last week's suspected poison gassing that reportedly killed hundreds of people in suburban Damascus.
Both friends and foes of the United States are demanding proof that the regime of Syrian President Bashar al-Assad gassed its own people, and the intelligence report, as well as the U.N. inspectors, were expected to provide more details as Washington tries to build an international coalition for a military response.
However, diplomatic and political developments this week raised the chances of the United States going it alone.
A U.N. Security Council meeting on Syria ended in deadlock Thursday, and Secretary-General Ban Ki-moon will try again to find consensus on a U.N. response when he meets Friday with the panel's five permanent members.
So far, opposition to any military response by Syrian ally Russia has scuttled U.N. action.
Overnight, Great Britain's Parliament voted down a proposal on taking part in a military response. The outcome was a blow to Obama's hopes of getting strong support from key NATO allies and some Arab League states if Russia undermined a U.N. resolution as expected.
A regional NATO ally, Turkey, on Friday backed the U.S. contention that al-Assad's regime was responsible for the chemical attack.
"The information at hand indicates that the opposition does not have these types of sophisticated weapons," said Turkish Foreign Minister Ahmet Davutoglu. "From our perspective, there is no doubt that the regime is responsible."
Meanwhile, doubts about military intervention also have escalated in the U.S. Congress, where legislators from both parties demand more answers from the Obama administration and some reject any U.S. military response.
In Washington, U.S. Secretary of State John Kerry was scheduled to speak about Syria at the State Department on Friday at 12:30 p.m. ET.
Before that, Obama met with his National Security Council to discuss the Syrian chemical attack, a White House official told CNN on condition of not being identified.
Alone or together?
The White House has made clear that the United States will respond in some form to the Syrian use of banned chemical weapons, but said Obama was still deciding exactly what to do.
Previously, the White House ruled out U.S. troops on the ground or imposing a no-fly zone. Sources have indicated limited strikes by cruise missiles based on U.S. naval ships in the region, targeting military command centers but not chemical weapons stockpiles, were the likely option.
However, the British Parliament's vote and demands by other key European allies, including France and Germany, to put off a decision until after the U.N. inspectors report on what happened in Syria have slowed the response time.
French President Francois Hollande told Le Monde newspaper Friday that intervention should be limited and not include al-Assad's overthrow, a position also expressed by Obama.
After the British development, a senior U.S. official, speaking on condition of anonymity, told CNN that going it alone was a real prospect.
"We care what they think. We value the process. But we're going to make the decision we need to make," the official said.
On Friday, former President George W. Bush said Obama's "got a tough choice to make."
"I was not a fan of Mr. Assad. He's an ally of Iran, he's made mischief," Bush told Fox News on Friday. "If he (Obama) decides to use the military, he's got the greatest military in the world backing him up."
Also Friday, another Obama predecessor, former President Jimmy Carter, said "a punitive military response without a U.N. Security Council mandate or broad support from NATO and the Arab League would be illegal under international law and unlikely to alter the course of the war."
U.S. Defense Secretary Chuck Hagel has repeatedly said the U.S. will respond to Syria in concert with allies.
"Our approach is to continue to find an international coalition that will act together," he told journalists Friday in Manila, the Philippines.
Skeptics of military action have pointed at the decision to use force in Iraq, where the United States government under Bush marched to war based on a thin claim that former dictator Saddam Hussein was harboring weapons of mass destruction.
Opponents are conjuring up a possible repeat of that scenario in Syria, though the intelligence being gathered on the use of WMDs in Syria may be more sound.
An NBC News poll conducted Wednesday and Thursday indicated that 50% of the public says the United States should not take military action against Damascus in response to the Syrian government's alleged use of chemical weapons against its own citizens, with 42% saying military action is appropriate.
But the survey suggested that if any military action is confined to air strikes using cruise missiles, support rises.
Supporters of a strong U.S. response say that no further proof is needed that the Syria regime was responsible.
"Come on. Does anybody really believe that those aren't chemical weapons -- those bodies of those children stacked up?" Republican Sen. John McCain of Arizona said Thursday on CNN.
Al-Assad's government has claimed that jihadists fighting with the opposition carried out the chemical weapons attacks on August 21 to turn global sentiments against it.
McCain doesn't buy it.
"The rebels don't have those weapons," he said. Similar arguments have been made by U.S. and foreign officials.
Democrats say Obama needs to make the case to Congress that al-Assad's regime was responsible and that a possible intervention won't get out of hand.
"The action has to have a very limited purpose, and the purpose is to deter future use of chemical weapons," Democratic Rep. Chris Van Hollen of Maryland told CNN.
Haunted by Iraq
Britain's Joint Intelligence Committee has concluded it was "highly likely" that Syrian government forces used poison gas outside Damascus last week in an attack that killed at least 350 people, according to a summary of the committee's findings released Thursday.
Before military intervention got voted down, Prime Minister David Cameron had said his government would not act without first hearing from the U.N. inspectors and giving Parliament another chance to decide the matter. But his opposition seemed to be reminded of the Iraq war.
"I think today the House of Commons spoke for the British people who said they didn't want a rush to war, and I was determined we learned the lessons of Iraq, and I'm glad we've made the prime minister see sense this evening," Labour Party leader Ed Miliband told the Press Association.
Though Cameron did not need parliamentary approval to commit to an intervention, he felt it important "to act as a democrat, to act a different way to previous prime ministers and properly consult Parliament," he said Friday.
He regrets not being able to build a consensus of lawmakers, he said.
Lack of support for military intervention at the United Nations was less of a surprise, due to Russia's known opposition.
"Russia is against any resolution of the U.N. Security Council, which may contain an option for use of force," Deputy Foreign Minister Gennady Gatilov said Friday.
The U.N. weapons inspectors expected to be out of Syria by Saturday will brief Ban, who then will swiftly brief the Security Council on the findings.
At home, Obama is facing doubts in Congress, with more than 160 legislators, including 63 fellow Democrats, signing letters calling for either a vote or at least a "full debate" before any U.S. action.
The author of one of those letters, Democratic Rep. Barbara Lee of California, said Obama should seek "an affirmative decision of Congress" before committing American forces. Congress is in recess until September 9, though some members advocate returning early to debate the matter.
CNN's Barbara Starr, Lesa Jansen, Ben Brumfield, Elise Labott, Christine Theodorou, Holly Yan, Nick Paton Walsh, Jim Acosta, Max Foster and Bharati Naik contributed to this report.