Canada is open to increasing its sanctions against Russia and believes there's no place for Syria's president in the future of the war-ravaged country, Prime Minister Justin Trudeau said Monday.

The tough line came after a weekend of conversations with the leaders of France and Britain and as Trudeau toured both First and Second World War battlefields.

The U.S. and Britain are actively investigating whether Russia helped make possible last week's chemical weapons attack in Syria, which killed at least 70 people, including 10 children.

It is widely believed that President Bashar al-Assad's regime was behind the atrocity. The U.S. fired 59 Tomahawk cruise missiles into the air base where the attack was thought to have originated.

Moscow has stood by its ally and warned the Trump administration against any further action.

At the same time, British Foreign Secretary Boris Johnson is expected to push at a meeting of G7 foreign ministers in Rome on Monday for further sanctions against Russia, adding to ones imposed because of the crisis in Ukraine.

Trudeau says Canada stands ready to do what is necessary.

Strengthened sanctions?

"I think Russia needs to be made aware of its responsibility in the bloody actions last week by the Assad regime," Trudeau said at the end of his trip to France marking the 100th anniversary of the Battle of Vimy Ridge.

"And therefore, we are always open to working with our friends, allies and partners to send messages through sanctions and other means to Russia."

Prime Minister Justin Trudeau comments on the role of Russia, Iran and Syrian President Bashar Al-Assad in Syria's future. 1:20

He spoke by telephone on Sunday with British Prime Minister Theresa May and held face-to-face discussions with French President Francois Hollande.

G7 ministers will be sounding out U.S. Secretary of State Rex Tillerson on Monday about whether Washington is committing itself to regime change in Syria.

Removing Assad a U.S. priority

Over the weekend, Nikki Haley, the U.S. ambassador to the United Nations, told CNN that removing Assad is a priority.

Trudeau wouldn't go that far, but he said some form of regime change is inevitable.

"I think there's no question that the medium- and long-term future of a peaceful Syria no longer includes Bashar al-Assad."

British Defence Secretary Michael Fallon said his country's intelligence community is examining the evidence.

"We're making our assessments," Fallon told CBC News in an interview.

"We think it is highly likely that these chemical weapons — almost without a doubt now — that these chemical weapons were used by the [Assad] regime, and we can be sure of how this was done. But irrespective of how direct the Russian involvement was, Russia has tolerated the abuse by the regime of chemical weapons and the flouting of successive Security Council resolutions."

He held out hope that President Vladimir Putin might still take responsible action.

"Russia could have intervened much earlier to stop [their] use against the civilian population, women and children, and could still do so," said Fallon, who attended Vimy Ridge ceremonies on Sunday.

Trudeau said Assad needs to be held to account, and the international community needs to move "as quickly as possible toward peace and stability in Syria."

Liberal position criticized

Conservative foreign affairs critic Peter Kent accused the Liberal government of taking a soft stand against Syria and the complicity of Russia and Iran in Assad's attacks on civilians.

"The government has stiffened its position, but it's still all over the map and imprecise as to what Canada should be saying and doing," he said.

Green Party Leader Elizabeth May said Russia and Iran must play a key role in peace talks to develop a "shared way forward" by persuading Assad to agree to an orderly transition to a new government. She cautioned against any plan to oust him from power.

"You can't force him out through military interventions when they have no basis in international law," she said.

Opposition MPs give their take on Trudeau's support of the U.S. bombing of Syria and say what they think should happen next. 1:51

On the other side of the globe, the U.S. has diverted a carrier battle group to waters off the Korea peninsula in response to what officials in Washington describe as recent provocations, including missile tests.

"We are worried about the dangerous and unstable North Korean regime — period," said Trudeau. "This rogue regime in North Korea is a danger not only to the immediate region, but the entire world."

At one point during the media availability, Trudeau seemed to search for the right words to describe the regime in Pyongyang, eventually settling on fundamentally irresponsible, hoping "to not use a word like crazy."

Trudeau wouldn't say whether Canada was prepared to join the U.S. ballistic missile defence program - something that has been debated as part of the Liberal government's defence policy review.

He would only say Canadians expect their government to keep them safe.