Stephen Harper is heading to Ukraine to demonstrate solidarity just as Kiev's war with Russian-backed rebels escalates, but the Prime Minister is still balking at providing weapons to the ancestral home of more than 1.2 million Canadians.

Mr. Harper, on his final international trip before a federal election campaign begins, is stopping in Ukraine on his way to a tour of Europe that includes a Group of Seven meeting in Bavaria and an audience with the Pope in Rome. He leaves for Kiev on Friday morning.

Ukrainian President Petro Poroshenko on Thursday told his military to prepare for a possible "full-scale invasion" by Russia, a statement he made one day after the worst fighting with Moscow-backed separatists in months.

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February's Minsk ceasefire agreement governing eastern Ukraine is in tatters after a 12-hour firefight involving artillery on both sides on Wednesday. Kiev said rebels tried to take the eastern Ukrainian town Maryinka.

Over the past 15 months, Mr. Harper has pledged non-lethal aid, loan guarantees, satellite imagery and military trainers to Ukraine as it struggles to deal with separatists who want to create a "New Russia" within the country. He has also joined U.S. and European allies in slapping sanctions on cronies and supporters of Russian President Vladimir Putin.

The Ukrainian Canadian Congress, an influential lobby in Ottawa, says the resumption of intense fighting in Ukraine proves Canada and its military partners must take the next step. A report compiled after Wednesday's fighting by the Organization for Security and Co-operation in Europe, an international observer group, strongly suggests the violence was the result of a rebel initiative.

"This assault against Ukrainian forces and Russia's continued flagrant violations must be answered with a robust response from Ukraine's allies – Canada, the United States and NATO countries," said Paul Grod, president of the Ukrainian Canadian Congress.

Mr. Grod, who is accompanying Mr. Harper to Kiev, is calling on Canada and its allies to "immediately provide Ukraine with defensive weapons, including anti-tank weapons" to defend its territory and population. NATO member countries have hesitated to make a commitment of this kind that would draw them even more squarely into a conflict with Russia.

Asked to respond to the request on Thursday, the Prime Minister said a decision on lethal aid would be "only made in concert with our allies."

What Mr. Harper did offer, though, was more tough talk – saying Russia should not be allowed back in the Group of Seven industrialized nations as long as Mr. Putin is President. G7 countries ejected Russia last year after Moscow annexed Ukraine's Crimean peninsula.

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"I don't think Russia under Vladimir Putin belongs in the G7. Period," Mr. Harper said, arguing the President, who as recently as last November maintained that Russian troops are not in Ukraine, cannot be trusted to tell the truth.

"This is kind of typical Russian foreign policy to just say black is white even though everyone knows the contrary. I think as long as that's the view that they are going to take, that they're just going to treat us like we are all stupid, there really is no point in having a dialogue with them."

Mr. Grod said he thinks a major and prolonged resumption of hostilities in eastern Ukraine would be the tipping point for Western countries that are still hesitating to deliver weaponry to Kiev.

"I don't think we will see weapons unless there is a significant renewal in fighting," he said.

He said such a decision would likely turn on what U.S. President Barack Obama does.

"Harper is waiting for Obama. If Obama says go, I think, frankly, it's a no brainer," Mr. Grod said.

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"There is overwhelming support for it in the U.S Congress and the challenge is the President."

With reports from Oliver Sachgau, Associated Press and Reuters

With reports from Oliver Sachgau, Associated Press and Reuters