German Chancellor Angela Merkel said: "We are in agreement that a return of Russian Federation to the G7 can not happen unless substantial progress is made in terms of the problems with Ukraine".
Other countries "have been taking advantage of the United States on trade", Trump said, laying out his fundamental grievance as he joined leaders of major industrialized nations assembled at a Canadian resort for the annual meeting.
He later said that Russia's return to the group would be "an asset" and that it would be a good move for peace in the world.
The two-day summit in Canada has been marred by fears of a trade war and tit-for-tat exchanges of hostile tweets, with United States trading partners furious over Mr Trump's decision to impose tariffs on steel and aluminium imports from Canada, the European Union and Mexico as part of his "America First" agenda.
President Donald Trump told foreign leaders at the Group of Seven summit that they must dramatically reduce trade barriers with the United States or they would risk losing access to the worlds largest economy, delivering his most defiant trade threat yet to his counterparts from around the globe. Mexico slapped a 25% import tariff on USA steel products, as well as 20% on pork products, 25% on bourbon and duties on other agricultural goods including cranberries.
G7 leaders, led by Prime Minister Justin Trudeau, Germany's Angela Merkle and French President Emmanuel Macron confronted Mr. Trump with a slew of data on import and exports to sway his thinking, but the President was unmoved.
That leaves Trump diametrically opposed with Canada, which says renegotiating the deal every five years would create perpetual uncertainty and harm long-term investment.
The leaders came armed with an array of their own statistics aimed at demonstrating to Trump that he was not right to view the U.S.as a victim.
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Trudeau refused, and the meeting was off the table, but the lead ministers from both countries talked trade on the sidelines of the G7 leaders' talks on Friday.
The US president has made it clear he believes the removal of tariffs against his G7 allies should come at a price - and he doesn't expect the US to pick up the tab.
Asked whether she was concerned the President could pull out of the trip if a trade war with the European Union escalates, Mrs May said Mr Trump had said was looking forward to the trip.
"The European Union is brutal to the United States".
Canadian Prime Minister Justin Trudeau insists the Trump hard line will only hurt the U.S. "And it's going to stop. Or we're going to make a deal directly with Canada, directly with Mexico", Trump said.
Sticking points also remain in the North American Free Trade Agreement (Nafta) renegotiations between Canada, the USA and Mexico, despite it being a key topic during the bilateral meeting between Mr Trump and Canadian PM Justin Trudeau.
The White House did not immediately respond to requests for comment on the official's remarks about Trump.
Speaking about Russia's military incursion in Crimea, a peninsula that was part of Ukraine, Trump on Saturday blamed President Obama for the annexation.
"We are like the piggy bank that everyone is robbing and that ends", he told a news conference before flying to Singapore for denuclearzation talks with North Korean leader Kim Jong-un.