BUENOS AIRES, Argentina -- Prime Minister Justin Trudeau spoke with Ukrainian President Petro Poroshenko on Thursday as pressure mounts on Canada to forge a united diplomatic front against Russian aggression in Ukraine.

Trudeau and Poroshenko spoke following the prime minister's arrival at the G20 summit in Buenos Aires on Thursday and the leaders discussed Russia's actions that resulted in the seizure of three Ukrainian naval vessels near Crimea, according to the Prime Minister's Office.

The call came after Russia announced Wednesday it would deploy another battery of anti-aircraft missiles to the Crimean Peninsula, bolstering its hold on the region it seized from Ukraine in 2014.

Top Ukrainian officials are now urging Trudeau to be a voice against Russia.

The issue has also become even more complicated in the past 24 hours due to developments in the United States, prompting Donald Trump to cancel a planned meeting with Vladimir Putin.

Trump announced Thursday on Twitter he would not be meeting Putin because "the ships and sailors have not been returned to Ukraine from Russia."

Andriy Shevchenko, the Ukrainian ambassador to Canada, said Trudeau should use his position as G7 president to deal with the current crisis.

Canada could also use this week's G20 meeting in Argentina to advance that line of response, Shevchenko said.

"We would like to see a joint consolidated response from the free world," he said.

In a primer published on the G20 summit, former Canadian diplomat Colin Robertson and vice president with the Canadian Global Affairs Institute said Trudeau must see if he and Freeland can find consensus among G7 fellow leaders on Russia's recent actions in Ukraine and on human rights abuses by Saudi Arabia.

"Neither is likely to happen," he wrote.

German Chancellor Angela Merkel said Thursday she plans to press Putin at G20 summit to urge the release of the Ukrainian ships and crews and to de-escalate the situation.

"We can only resolve this in talks with one another because there is no military solution to all of these conflicts," she said.

With files from Mike Blanchfield and The Associated Press