Prime Minister Justin Trudeau had a conversation with U.S. President Donald Trump "on the margins" of the NATO summit in Brussels Wednesday.

During the unofficial bilateral meeting, the pair discussed trade, including NAFTA, the Prime Minister's Office said without elaborating further. Trudeau and Trump also discussed the new Mexican President Andres Manuel Lopez Obrador.

An official described the closed-door conversation as “positive,” The Canadian Press reported.

The NATO summit is the first time Trudeau and Trump have been face-to-face since Canada levelled retaliatory tariffs on U.S. goods, over its steel and aluminum tariffs on Canada.

It was also their first in-person meeting since the G7 which ended in acrimony and was followed by Trump and members of his administration levelling personal attacks at Trudeau, including Trump calling the prime minister "very dishonest and weak" in a tweet. Trump’s blunt criticism came after Trudeau said Canada won’t be “pushed around” by the U.S. on trade.

Despite the recent flare-ups, the two leaders avoided a public confrontation Wednesday. During a photo-op, Trudeau stood to the side as Trump chatted with other leaders, including Britain's Theresa May and NATO Secretary General Jens Stoltenberg.

Instead, Trump directed his ire at German Chancellor Angela Merkel, accusing her country of being “totally controlled” and “captive to Russia” because Germany has a pipeline deal with its easterly neighbour.

Merkel responded by insisting that Germany makes its own policies and decisions.

Trump levelled a more general broadside at NATO allies, accusing them once again of not meeting defence spending commitments. Trump suggested ally countries spend four per cent of their GDP on defence, which is double the existing NATO goal of two per cent by 2024.

The U.S. itself does not meet the four per cent mark. According to the Pentagon, the U.S. spends 3.3 per cent of its GDP on defence.

The Trudeau government has vowed to increase defence spending by 70 per cent over the next 10 years. Even after that investment, Canada would still fall short of the goal and only reach 1.4 per cent by the deadline.

Ahead of the NATO meeting, Trump sent a letter to Ottawa expressing “growing frustration” about the shortfall.

Trudeau downplayed the importance of the defence spending goal on Tuesday, calling it a “limited tool” to gauge a country’s NATO commitment.

By calling out NATO allies on underspending, Trump is doubling down on the same approach that got him elected, said Larry Haas, a senior fellow with the American Foreign Policy Council.

“This is really a reflection once again of his kind of America-first, nativist, isolationist perspective on the world. And at its heart, it goes to Donald Trump’s view that when someone else wins, America loses. And when America wins, someone else loses,” Haas told CTV News Channel on Wednesday.

“His world view is very zero sum.”

While NATO spending appears to be Trump’s latest frustration, former Trump presidential campaign advisor Sam Nunberg said NATO spending was on the president’s radar long before the 2016 election.

“I can tell you having worked with him from 2011 to mid-2015, NATO was a major subject of his,” Nunberg told CTV News Channel.

The summit ends Thursday after a final day of meetings.

With files from The Canadian Press and The Associated Press