Stephen Harper told Russian President Vladimir Putin flatly that he needs "to get out of Ukraine," when the two met at a Group of 20 summit of major economies in Brisbane.
A spokesman for the Canadian Prime Minister relayed the details of the encounter and, according to director of communications Jason MacDonald, "Mr. Putin did not respond positively."
Mr. Harper and leaders of other Group of 20 economies are meeting on Australia's northeast coast to find ways of spurring growth and creating jobs, but the debate is quickly taking on a more familiar theme: what to do about Russia.
Mr. Putin had arrived at the summit in an unrepentant mood Friday just as the North Atlantic Treaty Organization was offering detailed reports on the troops and heavy weaponry Moscow is sending into eastern Ukraine, a violation of a ceasefire agreed to in September.
Mr. Putin, whose country has been feeling the effects of Western sanctions for months after annexing Crimea, accused the West of imposing unlawful penalties on Russia and said Moscow is prepared, if necessary, to wait out a "catastrophic" collapse in oil prices.
The Russian leader said the asset freezes, visa bans and measures preventing Russian companies from accessing Western financial markets and technology went against international law because only the United Nations had the right to impose them.
Mr. Harper's encounter with Mr. Putin came Saturday morning when the Canadian Prime Minister was speaking to a group of leaders.
The Russian Leader stuck out his hand.
Mr. Harper accepted the gesture but said to the Russian Leader: "I guess I'll shake your hand but I have only one thing to say to you, you need to get out of Ukraine."
World leaders on Ukraine
British Prime Minister David Cameron, meanwhile, warned Russia will face even greater sanctions if it does not alter course in Ukraine.
"If Russia takes a positive approach toward Ukraine's freedom and responsibility, we could see those sanctions removed; if Russia continues to make matters worse, then we could see those sanctions increased. It's as simple as that," Mr. Cameron told reporters in Canberra, Australia's capital.
Mr. Putin used an ostentatious display of naval might to draw more attention this week, sending a convoy of four Russian ships steaming toward Brisbane, even while remaining in international waters.
German Chancellor Angela Merkel played down any threat posed by the warships but joined other Western leaders in speaking out against Mr. Putin's conduct in Ukraine.
"What is concerning me quite more is that the territorial integrity of Ukraine is being violated and that the agreement of Minsk is not followed," she said, referring to the truce accord.
Australian Prime Minister Tony Abbott, who wants to redirect discussion back to economic matters, sounded exasperated Friday. "Russia would be so much more attractive if it was aspiring to be a superpower for peace and freedom and prosperity, instead of trying to recreate the lost glories of tsarism or the old Soviet Union."
Putin vs. G20
Fen Hampson, director of the Global Security and Politics program at the Centre for International Governance Innovation in Waterloo, Ont., said Mr. Putin appears to be trying to divide G20 members.
"What he may be trying to do is drive a wedge in the G20 between those who support Russia and those in the West who don't," Mr. Hampson said.
Although the more exclusive Group of Seven club of nations has kicked Russia from its ranks over Crimea, there is less unified thinking in the broader G20, which includes rapidly developing countries, such as Brazil, Russia, China and India.
Australia consulted G20 members on whether Russia should be excluded from the meeting after the Crimean invasion but did not find a consensus.
Mr. Putin is vulnerable, though. "His foreign policy strategy is politically popular; the financial market impact of sanctions is not, and Russia faces big fiscal problems owing to that, and owing to the collapse in energy commodity prices," Finn Poschmann, vice president of policy at the CD Howe Institute, said.
"Sharp, heavy sanctions do have an impact, and unified G20 sentiment on this would too," he said. "That is the stick -- but Mr. Putin cannot easily back down, for obvious reasons. However, a clear set of negotiated conditions, in return for a speedy end to sanctions, would help."
The G20 succeeded in its initial efforts to address the world financial crisis, but most of the continuing work on that front is the purview of central bankers.
Mr. Hampson says the G20 has been far less successful dealing with the macroeconomic and fiscal issues because these are heavily politicized areas of national responsibility. G20 leaders are trying to find ways to meet a pledge to increase their economies' combined growth by two percentage points by the end of 2020.
Mr. Abbott has vowed this meeting "will not be a talkfest" and is proposing several measures, including a "global infrastructure hub" that would help match projects with investors by cutting regulatory hurdles.
The world's top infrastructure banks have applauded the move.
Mr. Harper, who has announced his government will balance Ottawa's books next year after a string of deficits, is expected to offer G20 colleagues his insight into fiscal reform and his trade agenda.
With reports from Reuters, AP, Agence-France Press and Bloomberg News