Western countries are presenting a high-stakes ultimatum to Russia: Allow regime-change in Syria and cut loose Bashar Assad, or remain a pariah moored on the fringes of the international community.

Different U.S. allies articulated different versions of that warning Tuesday, including Canada. During a G7 meeting in Italy, Foreign Affairs Minister Chrystia Freeland urged Russia to seize the moment as a chance to break with Assad.

The twin events of a horrific chemical attack on Syrian civilians, combined with U.S. airstrikes, have created new momentum in pursuing a long-term political solution to the Syrian civil war, Freeland told a conference call.

"Russia needs to decide whether it wants to double down on its support of a murderous regime that is committing war crimes, or whether right now it wants to say, 'You know what? We do not want to be associated with this, this is not where we want our country to be,'" she said.

"I really do hope Russia will take this opportunity to be on the right side of history."

The violence in Syria has brought to a boiling point years of escalating tension with Moscow — the tension surged with the invasion of Ukraine in 2014, followed by painful economic sanctions, and then divergent views on Assad.

The U.S. is now hinting that a shift in Syria posture could de-escalate things.

The point was delivered with a twist of mockery from the White House. A spokesman for President Donald Trump insinuated that Russia's behaviour of recent years had left it confined to an international alliance of losers.

"Russia is isolated. They have aligned themselves with North Korea, Syria, Iran. That's not exactly a group of countries you're looking to hang out with. With the exception of Russia, they are all failed states," Sean Spicer said.

"Russia is on an island.... This is not a team you want to be on."

It certainly didn't sound like Russia was tempted by the notion of a strategic reset Tuesday. In public comments, President Vladimir Putin exhibited no inclination toward a pro-western, anti-Assad pivot.

In fact, Putin appeared to accuse the West of making up some chemical attacks in Syria. He even likened it to the false evidence presented by the U.S. that led to the invasion of Iraq in 2003.

Putin called them false flags.

"We have reports from multiple sources that false flags (are happening)... They plan to plant some chemical there and accuse the Syrian government of an attack," he said, according to Russia Today.

He made those remarks during a visit from Italy's president, and before another high-profile visit. U.S. Secretary of State Rex Tillerson landed in Moscow on Tuesday after the G7 meetings.

Tillerson previewed the message he would take to Moscow. A former oil executive with good relationships in Russia, he appeared to suggest Moscow had a strategic opportunity here: to repair strained relationships with other world powers.

"Russia has really aligned itself with the Assad regime, the Iranians, and Hezbollah. Is that a long-term alliance that serves Russia's interest, or would Russia prefer to realign with the United States, with other Western countries and Middle East countries who are seeking to resolve the Syrian crisis?"

The G7 ministers blamed Assad's military for a deadly chemical attack last week.

However, there were some differences among the group. British Foreign Secretary Boris Johnson said the G7 was considering new sanctions on Russian military figures to press Moscow to end military support for Assad, but the proposal was not adopted.

There also were different noises out of Moscow.

A prominent Russian lawmaker said his country had no intention of getting pulled into combat with United States. That came a day after a pro-Assad military coalition said it might fire back if the U.S. strikes again.

Viktor Ozerov, the head of the defence and security committee in Russia's upper house, said Russia's enemy in Syria will continue to be terrorist rebels: "Russia does not intend to get involved in an armed standoff with the United States there," he was quoted saying by RIA Novosti.

As for Canada, the Opposition wants to hear more about this country's role. In an interview, interim Conservative leader Rona Ambrose said she wants details about what the government intends — either diplomatic or otherwise.

''The question we have to ask now is, if the prime minister supports the removal of Assad... what does that look like for Canada?" Ambrose said in an interview with The Canadian Press.

"As parliamentarians, we need to ask that question. What role will Canada play? What does that mean on a practical level?"

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AND what happens to Syria , after Assad ?