The president of the European Council sounded an ominous warning for the G7 as leaders of the world's major democracies began arriving Saturday in the French seaside resort of Biarritz for their annual summit.

Donald Tusk did not mince words about the state of discord among nations and whether there is enough political will to address the rise of authoritarian states, halt emerging trade wars and fight the disastrous effects of climate change.

"This may be the last moment to restore our political community," said Tusk, the former prime minister of Poland who has headed the European Council since 2014.

"This will be another G7 which will be a difficult test of unity and solidarity of the free world and its leaders."

It is far from certain, he said, whether the 44-year-old international institution will be able to find common solutions or if the nations will "focus on senseless disputes amongst each other."

Since last year's summit in Charlevoix, Que., it has become even more difficult for countries to find a common language.

WATCH: Donald Tusk addresses the G7

The European Council president offered an ominous warning about the need for world leaders to work together. 0:46

Later on Saturday, Prime Minister Justin Trudeau sat down with new British Prime Minister Boris Johnson.

In French remarks, Trudeau said the global economy and trade would be a big focus of their private meeting, as well as climate change.

Johnson replied that he couldn't think of any big issues on which Canada and Britain disagree.

"Canada and U.K. are side by side," he told reporters.

However, this week Canada rebuked its cross-Atlantic neighbour for revoking the citizenship of Jack Letts, dubbed Jihadi Jack by British media after he left for Syria and is alleged to have joined ISIS.

Prime Ministers Boris Johnson and Justin Trudeau meet at the G7 summit in Biarritz, France. (Stefan Rousseau/Getty Images)

Letts, who is currently in a Kurdish prison, also holds Canadian citizenship and has now expressed a desire to come to Canada.

Public Safety Minister Ralph Goodale said the Britain was unilaterally trying to "offload their responsibilities" by revoking its citizenship. Many countries are facing a quandary of how to deal with their nationals picked up in ISIS territory.

A federal source close to the discussions on Saturday said that Trudeau brought up the Letts issue with Johnson and reiterated Canada's displeasure.

With Brexit at the top of their agendas, European leaders took advantage of a small window of time before the official start of the G7 summit to meet with Johnson.

The European leaders met separately on Saturday afternoon, including Johnson, EU Council President Tusk, Germany's Angela Merkel, France's Emmanuel Macron and Italy's caretaker leader Guiseppe Conte.

The issue of European countries ratifying the Comprehensive Economic Trade Agreement (CETA) has been percolating around the summit. The French National Assembly ratified it last month, but it faces an uncertain vote in the country's senate this fall.

Concern over CETA in France

The French senate is controlled by conservatives who are opposed to Macron and are widely expected to vote against him, principally over objections to Canadian beef imports.

Canada's ambassador to France, Isabelle Hudon, said it's unclear which way it will go. There is a part of France that is deeply skeptical about the trade deal and she sees it as her mission to have people and companies better understand it.

"One thing I realized moving in France is that in Canada we are way much more comfortable doing trade, our companies are more comfortable doing international trade," she said. "There's a steep curve in France around trade issues and we're there to explain."

Demonstrators use a part of a barricade to attack the police blockade during a protest against G7 summit. (Sergio Perez/Reuters)

Thousands of anti-globalization and environmental activists joined yellow vest protesters and Basque separatists on Saturday near Biarritz to demand action from G7 leaders.

The peaceful protesters converged on the nearby town of Hendaye on the French border with Spain to demand change in the economic and climate policies pursued by the world's leading industrial nations.

'Tremendous' trade with Japan

Trudeau also met with Japanese Prime Minister Shinzo Abe. The two were set to talk trade and security.

"Canada and Japan have had a tremendous trade relationship," Trudeau said, adding that Abe has been a strong leader on many issues that also matter to Canada.

The Japanese leader responded that this is an opportunity to successfully send out a powerful message on various global challenges.

Japan's Prime Minister Shinzo Abe and Canada's Prime Minister Justin Trudeau arrive for a family photo at the G7 summit. (Yves Herman/Reuters)

Canadian officials are expecting an update on the Trans-Pacific Partnership trade deal. but Japan is also eager to talk security.

Canada recently committed to a regular rotation of warships in the Far East to keep an eye on North Korean sanctions.

In recent days, an intelligence-sharing partnership between Japan and South Korea fell apart over a trade dispute. And according to Japanese officials, speaking on background to CBC News, the cancelling of the arrangement puts the alliance against North Korea in danger.

Trudeau hosted last year's summit, which ended with Trump tweeting insults at him from aboard Air Force One because he felt he had been slighted by the PM after he left the meeting.

Trump threatens tariffs on French wine

Only hours before his arrival in Biarritz, President Donald Trump had threatened anew to place tariffs on French wine imports to the U.S. in a spat over France's digital services tax; the European Union promised to retaliate. That was the backdrop for a late addition to his summit schedule — a two-hour lunch with French President Emmanuel Macron outside the opulent Hotel du Palais.

Prime Minister Justin Trudeau arrives in Biarritz on Friday to attend the G7 summit. (Sean Kilpatrick/The Canadian Press)

The summit host said the two men were discussing "a lot of crises" around the world, including Libya, Iran and Russia, as well as trade policy and climate change.

But he also echoed Trump's calls for Europe to do more to address the global slowdown, including by cutting taxes. "When I look at Europe, especially, we need some new tools to relaunch our economy," Macron said.

Trump insisted that despite tensions, he and Macron "actually have a lot in common" and a "special relationship." In a later tweet, he said: "Big weekend with other world leaders!"

Russia not invited

Tusk dismissed Trump's recent second attempt to convince the other countries to allow Russia to return to the summit table, restoring the G8. Tusk noted that Moscow has yet to return Crimea to Ukraine and maintains an aggressive posture toward its neighbours.

"The reasons Russia was disinvited in 2014 are still valid. There are new reasons, such as the Russian provocation on the Azov Sea," he said, referring to the seizure of Ukrainian patrol boats and sailors in the Kursk Strait late last year.

In the 1990s, Russia was invited because it was on the path toward liberal democracy, a free-market economy and human rights protections.

"Is there anyone among us who can say with full conviction — not out of business calculation — that Russia is on that path?" Tusk said.

It would be better to invite Ukraine as a guest next year, as opposed to Russia, he added.