U.S. President Barack Obama says he hasn't made a final decision about a military strike against Syria, but he says he's considering a limited and narrow action in response to a chemical weapons attack that he says Syria's government carried out last week.  

Speaking Friday in televised remarks from Washington, Obama said the Aug. 21 attack was a challenge to the world and threatens U.S. national security.   

Obama's comments came after the U.S. released an intelligence assessment that found with "high confidence" that Syrian President Bashar al-Assad's government carried out a chemical weapons attack last week.  

The U.S. says the attack killed more than 1,400 people.  

"We are looking at the possibility of a limited, narrow act" intended to deter the use of chemical weapons, Obama said. "We're not considering any open-ended commitment. We're not considering any 'boots on the ground' approach."

Kerry calls attacks 'crime against humanity'

His remarks follow those of U.S. Secretary of State John Kerry, who said Syria's government committed a "crime against humanity" in what he described as a planned chemical attack in the Damascus area last week, but he gave assurances that U.S. military retaliation would not be a repeat of "the Iraq experience."

Kerry said nearly a third of the 1,429 Syrians who died were children, and alleges the U.S. has proof that the Aug. 21 attack was undertaken by the Assad regime

"I'm not asking you to take my word for it. Read for yourself, everyone…the evidence from thousands of sources, evidence that is already publicly available," he said.

Kerry added that U.S. intelligence sources have "carefully reviewed and re-reviewed" evidence, and were "mindful of the Iraq experiences" and will not repeat that mistake. 

"This morning's release of our government's unclassified estimate of what took place in Syria is so important. Its findings are as clear as they are compelling," he added. "We know that for three days before the attack, the Syrian regime's chemical weapons personnel were on the ground, in the area, making preparations."

In laying out his case for a military response in Syria, Kerry described the debate as a defining moment for America, which has "always tried to honour a set of universal values."

The alleged deployment of poison gas, he charged, is an international war crime that cannot go unanswered.

"This crime against conscience, this crime against humanity, this crime against the most fundamental principals of international community, against the norm of the international community — this matters to us," Kerry said.

Despite roadblocks in forming an international coalition, including the stunning decision by the British Parliament on Thursday to keep the U.K. on the sidelines in any international military action, Obama appeared undeterred. Advisers have previously said he would be willing to retaliate against Assad on his own.

After Kerry spoke, Foreign Affairs Minister John Baird reiterated Friday that Canada has "no plans at this time for a Canadian military mission" but said the government supports allies responding to "the Assad regime's horrific attack on its own people."

"The Obama administration has shown great resolve and proper due diligence in the past week, and we fully support its efforts going forward," a statement from Baird said.

Canada won't be involved in military action

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Canadian Prime Minister Stephen Harper says Canada is not planning to get involved in any military action in Syria. (Reuters)

Prime Minister Stephen Harper said Thursday that Canada is a "reluctant convert" to the idea that Western military action might be necessary to punish Syria for its alleged use of chemical weapons.

However, Canada will not have a military mission in any strike against Syria's government, even though it endorses some kind of "forceful action."

The illegal use of chemical munitions is a "very big risk" to the international community, Harper said, and it can't be ignored.

"We do support our allies who are contemplating forceful action to deal with this," he said. "That said, at the present time the government of Canada has no plans, we have no plans of our own, to have a Canadian military mission," Harper said in Toronto.

Talk of international military action against Syria comes as United Nations inspectors completed their final day of investigations into the alleged use of chemicals in a Damascus-area attack last week. The team has spent the past week touring rebel-controlled areas to collect evidence of a suspected poison gas attack on opposition fighters on the outskirts of the capital.

On Friday, UN inspectors toured a government-held area, visiting troops at the Yousef al-Azma military hospital, a witness told Reuters. The Assad regime claims that patients were affected by chemical munitions released by the rebels.

Western powers such as Britain, France and the U.S. allege that the only side capable of unleashing such chemical munitions is the government — a charge that Assad denies.

The UN team appeared to be on their way out of Syria early Saturday, according to a Reuters witness.

The witness saw the team's convoy of vehicles head onto a highway that leads to neighbouring Lebanon. They are meant to immediately present their findings to UN Secretary General Ban Ki-moon.

U.S. posts Syria intelligence assessment

Friday's statements came as the U.S. government released a short intelligence assessment laying out its case for asserting that Assad's regime used chemical agents to kill civilians. The brief report, which excludes classified information, was posted on the U.S. State Department's website.

Throughout, the U.S. government says it has "high confidence" that the Syrian government carried out the attack, saying the regime has a stockpile of chemical weapons and the ability to carry out an attack of the magnitude seen last week.

"Multiple streams of intelligence indicate that the regime executed a rocket and artillery attack against the Damascus suburbs in the early hours of Aug. 21," the assessment says, citing human intelligence, signal intercepts, social media reports, videos, interviews and satellite detections.

The U.S. report said they had "no indication" that the opposition carried out a "large-scale co-ordinated rocket and artillery attack" like the one reported in Damascus. Further, the report says the U.S. does not believe opposition forces have the ability to fabricate all of the videos and physical symptoms verified by doctors and charity groups.

The report does not reveal its methods or name any officials, but it does say that the U.S. intercepted communications from a senior official "intimately familiar with the offensive who confirmed that chemical weapons were used by the regime on Aug. 21 and was concerned with the UN inspectors obtaining evidence."

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A woman shouts slogans during a demonstration against military strikes on the Syrian government and to show their support for the regime of Syria's President Bashar al-Assad, after Friday prayers in Jordan. (Majed Jaber/Reuters)

It is not certain if the U.S. will have to act alone should it proceed with a military response. France announced that its armed forces "have been put in position to respond" if President François Hollande commits forces to intervention against Syria. Hollande does not need French parliamentary approval to launch military action that lasts less than four months.

Susan Ahmad, an anti-Assad activist in Syria, told CBC News her feeling is that Syrians are so desperate to see Assad toppled after two years of civil war that they would welcome a U.S. strike.

"Nobody likes any foreign intervention in their own country, but we have been suffering for more than two years now," Ahmad told CBC News from Damascus.

"Assad has been shelling cities, killing innocent people … so what we want — if that strike is going to happen — we want it to finish Assad, we want it to finish that war in Syria," she said.

U.S. intelligence no 'slam dunk,' source says 

Earlier, U.S. officials said the intelligence assessments are no "slam dunk," with questions remaining about who actually controls some of Syria's chemical weapons stores and doubts about whether Assad himself ordered the strike.

The officials spoke on condition of anonymity because they were not authorized to discuss the intelligence publicly.

Obama spent much of the week making a case for a robust response to world leaders, speaking Thursday with German Chancellor Angela Merkel. With national elections scheduled in Germany for next month, Merkel is unlikely to involve her country in a military conflict.

Merkel also discussed Syria by phone Thursday with Russian President Vladimir Putin, insisting that the attack "requires an international reaction," Merkel spokesman Steffen Seibert said.

Obama has ruled out putting American forces on the ground in Syria or setting up a no-fly zone over the country. He's also said any U.S. response to the chemical weapons attack would be limited in scope and aimed solely at punishing Assad for deploying deadly gases, not at regime change.

"We do have to make sure that when countries break international norms on weapons like chemical weapons that could threaten us, that they are held accountable," he said during a television interview aired earlier in the week.

The most likely military option would be Tomahawk cruise missile strikes from four U.S. navy destroyers in the eastern Mediterranean Sea.

At a minimum, Western forces are expected to strike targets that symbolize Assad's military and political might: military and national police headquarters, including the Defence Ministry; the Syrian military's general staff; and the four-brigade Republican Guard that is in charge of protecting Damascus, Assad's seat of power. Assad's ruling Baath Party headquarters could be targeted, too.

U.S. officials also are considering attacking military command centres and vital forces, communications hubs and weapons caches, including ballistic missile batteries

With files from CBC News