Canada was briefed in advance of the U.S. missile strike on an airbase in western Syria that the U.S. says was used by Syrian President Bashar al-Assad's forces to launch a chemical weapons attack Tuesday, said Prime Minister Justin Trudeau.

During question period in the House of Commons on Friday, Trudeau said Canada was informed about the bombing of the Shayrat airbase near Homs "about an hour before the airstrikes by the American military on Syria."

Trudeau said U.S. Secretary of Defence James Mattis called Defence Minister Harjit Sajjan Thursday night to tip Canada off, and Sajjan "immediately" briefed Trudeau.

On Friday, however, U.S. President Donald Trump's Press Secretary Sean Spicer seemed to present a different version of events.

"Missiles were launched at 7:40 p.m. during dinner," Spicer told reporters at the Tideline Hotel in Palm Beach, Florida. "Foreign leaders and congressional leaders were notified starting at 8:30 p.m., just as first impacts were hitting the ground."

It remains unclear if Canada was given warning in advance of other nations, but Trudeau repeated his earlier comments later in Dartmouth, N.S., saying Mattis called Sajjan an hour before the strikes.

Trudeau also said that while his government will continue to help Canada's allies fight terrorism and provide humanitarian assistance to the Syrian people that "Canada's military role in the region remains unchanged."

"We will continue to work to see how Canada can help," Trudeau said. "But right now Canadian military efforts are concentrated on continuing our mission in Northern Iraq."

The airstrike early Friday local time in Syria targeted the Shayrat military airbase in Homs. (CBC)

Trudeau spoke with U.S. President Trump on Friday morning. According to a readout of that call circulated by the Prime Minister's Office, Trudeau told Trump that Canada fully supports the "limited and focused action to degrade the Syrian regime's ability to conduct chemical weapons attacks."

During question period Friday, Conservative MP Pierre Poilievre criticized the Trudeau government for what he said were inconsistencies in the prime minister's response to the Assad regime's use of chemical weapons.

Poilievre noted that Trudeau's comments in New York on Thursday suggested that there were "continuing questions" about who exactly was responsible for the attack, pointing out that Trudeau said the UN Security Council should launch an investigation into who was behind the use of the deadly nerve toxins.

The Conservative MP said the rapid change in positions proves Canada has been "completely out of the loop" on developments in the region.

"Now [Trudeau] says he fully supports the United States' unilateral missile strikes against the Assad regime," Poilievre said in the House."The government's position seems to change with the wind."

Syria responsible says U.S.

Trudeau explained Friday, however, that the U.S. had provided him with information about the chemical attack in the northern Syrian town of Khan Sheikhoun.

"Secretary Mattis called Defence Minister Harjit Sajjan to confirm that Bashar al-Assad and his regime were responsible for the horrific attacks on civilians of a few days ago," Trudeau said.

"A trusted and reliable ally in the United States informed us that the Assad regime was responsible for these chemical attacks," Trudeau said in Dartmouth.

Earlier Sajjan told the House, "Assad's repeated use of chemical weapons must not continue." Both Trudeau and Sajjan said the Canadian government will continue to support a diplomatic resolution to the Syrian crisis.

Trudeau on US strike in Syria 0:45

In a statement issued Friday morning, interim Conservative leader Rona Ambrose said the Official Opposition supported "the efforts of the United States to prevent Syria's military from launching further chemical weapon attacks.

"The global community cannot sit idly by while deadly nerve toxins are unleashed on innocent civilians," the statement said.

NDP MP Murray Rankin said the Assad regime must be held responsible for these "shocking" crimes.

"Canada must also step up our efforts on the humanitarian front, particularly in the face of drastic cuts to UN programs planned by the Trump administration," he said.

Overnight missile strike

The United States fired cruise missiles at Syria overnight, in response to this week's chemical attack that killed more than 80 Syrian civilians in the province of Idlib.

The American missile strikes hit a government-controlled airbase in central Syria. U.S. officials say the airbase was the originating point for the plans behind Tuesday's gas attack.

On Wednesday and Thursday, Trudeau and Foreign Affairs Minister Chrystia Freeland made repeated statements condemning the chemical weapons attack, urging the international community to investigate the gas attack to confirm the Assad government was behind it.

Freeland said the chemical weapons attack raised "grave questions" about whether the Assad regime could work towards a political solution in Syria.

Friday's statement from Ambrose criticized the Trudeau government for offering "very little in terms of concrete action to hold the Russian-backed government of Syria accountable."

"Contrary to the prime minister's beliefs, the United Nations Security Council has proven itself woefully ineffectual when it comes to resolving the Syrian conflict," the Conservative statement said.