Writing on Twitter, President Trump said: "PM Justin Trudeau of Canada acted so meek and mild during our G7 meetings, only to give a news conference after I left saying that, "US tariffs were kind of insulting" and he "will not be pushed around".
She said: "The situation is not pleasant".
Trudeau's office cast doubt over the genuineness of Trump's offense at the prime minister's remarks, pointing out that Trudeau's messages simply reiterated his position before the summit, that he will oppose attempts to bully Canada on trade.
Trump and French President Emmanuel Macron had what was described by a French official as a "very cordial" discussion about trade and North Korea.
British Prime Minister Theresa May on Friday warned both Trump and the European Union of the dangers of entering a tit-for-tat trade war over tariffs, urging both sides to instead focus on China's excess steel production. Trump himself looks like a comically petulant child, and John Bolton, the National Security Advisor, appears to be nervous, staunchly standing by the president.
Merkel and Trump also had a brief conversation at the summit. The source did not say Trump explicitly said he wanted all German-made cars out of the US.
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Trump revoked his administration's support for the G7 communique after Trudeau's news conference.
Other G-7 countries lobbied unsuccessfully at the summit for the U.S.to reverse its tariffs on imported steel and aluminum imports.
Turning to Russia, Merkel said she could imagine Moscow re-joining the G7 format at some point, but there first had to be progress in the implementation of the peace plan for Ukraine. "They don't take our farm products", Mr Trump complained at the news conference. He has directed USA officials "not to endorse" the G-7 joint statement, and personally insulted Trudeau in a series of Twitter posts. Trump cited unfair trade and tariffs from Canada, a longtime U.S. ally, as one of the reasons he refused to back the joint statement.
"Actually, we were just talking, the whole group, about something unrelated to everything, very friendly".
The photo became a sensation online, and many observers felt it underscored the growing tension between Trump and the other G7 leaders.
"International cooperation can not be dictated by fits of anger and throwaway remarks", Macron said in a statement.