BUENOS AIRES, Argentina -- Prime Minister Justin Trudeau used face time with two of the world's most controversial leaders -- Russian President Vladimir Putin and Saudi Arabian Crown Prince Mohammed bin Salman -- to discuss concerns about issues unfolding under their watch.

In Buenos Aires on Saturday, Trudeau told a news conference that he directly pressed Putin about actions that resulted in the Russian seizure of three Ukrainian naval vessels near Crimea -- a message that top Ukrainian officials wanted Trudeau to relay.

Trudeau said he told Putin of the need to release imprisoned Ukrainian sailors during a meeting of world leaders on Friday, but there wasn't an opportunity for Putin to respond to the remarks.

"For me, it is obvious that this is an issue that concerns not just Canada but a number of our NATO allies," Trudeau said Saturday. "We are all very much hoping that there will be de-escalation and a release of those prisoners."

Trudeau's message to Putin came on the heels of a Friday statement from the foreign ministers of Canada, Germany, Italy, Japan, the United Kingdom and the United States, as well as the high representative of the European Union, expressing concern about Russia's actions against Ukraine in the Kerch Strait and surrounding waters.

Trudeau also indicated Saturday that he spoke directly with Saudi Arabia's crown prince on the sidelines of a dinner offered by Argentina that was held on Friday night.

"I took the opportunity to have a conversation with the crown prince directly, in which we discussed the diplomatic discord between Canada and Saudi Arabia," he said.

Trudeau said he also brought up the need for better answers on the killing of journalist Saudi journalist Jamal Khashoggi and the ongoing imprisonment of Raif Badawi, as well as the need for an immediate ceasefire and humanitarian aid in Yemen.

The civil war in Yemen constitutes the largest humanitarian catastrophe going on in the world today, Trudeau said, adding it is a subject that has been raised throughout the G20 summit.

"The situation is dire and getting worse," he said.

Trudeau stressed that he continues to believe "frank and direct" conversations with leaders matter, adding they are what Canadians expect him to do and what the world has come to expect of Canada.

Canada and other countries faced the difficulty of how to handle the presence of Saudi Arabia's crown prince, known by the initials MBS, at the G20 summit.

The trip marked the highest-profile overseas junket for the crown prince since Khashoggi's murder.

On Saturday, Trudeau also sat down separately with French President Emmanuel Macron and British Prime Minister Theresa May.

During both bilateral sessions, Trudeau discussed Khashoggi's October murder at the Saudi consulate in Istanbul and Canadian sanctions enacted on 17 Saudi nationals implicated in the killing.

Foreign Affairs Minister Chrystia Freeland announced on Thursday the federal government had looked closely at the involvement of each person it sanctioned and concluded they were either directly involved or complicit in the murder.

The sanctions freeze the targets' Canadian assets and make them inadmissible to Canada.

Earlier this month, the United States imposed its own sanctions on Saudi officials for the same reason.

Saudi Arabia is set to host the G20 summit in 2020.