Donald Trump withdrew his endorsement of the joint communique at the end of the G7 summit - after calling Canadian prime minister Justin Trudeau “dishonest and weak”.
The summit in Canada was marked by the US president’s controversial trade policy which has put him at odds with the rest of the G7 leaders.
He warned that retaliation against metal tariffs - 25 per cent on imports of steel and 10 per cent on aluminium from countries including the UK and the rest of the European Union - would be a mistake after previously calling the EU approach to business “brutal”.
Despite the differences, Mr Trudeau announced that the leaders had managed to agree a joint communique at the summit which highlighted the importance of “free, fair and mutually beneficial trade and investment” and said the G7 would “continue to fight protectionism”.
He said: “We had some strong, firm conversations on trade and specifically on American tariffs.”
But after saying he would give his relationship with fellow world leaders 10 out of 10, Mr Trump hit out at his northern neighbour.
He tweeted that he would not now endorse the communique due to “false statements” from the Canadian PM.
He wrote: “Based on Justin’s false statements at his news conference, and the fact that Canada is charging massive Tariffs to our U.S. farmers, workers and companies, I have instructed our U.S. Reps not to endorse the Communique as we look at Tariffs on automobiles flooding the U.S. Market!”
He added: “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.” Very dishonest & weak. Our Tariffs are in response to his of 270 per cent on dairy!”
During the meeting, Mr Trump accused other states of “robbing” his country through their trade policies and proposed scrapping tariffs across the G7.
But Theresa May hit back, branding the tariffs “unjustified” and saying the EU would respond - although she warned against further tit-for-tat escalation.
Despite the tensions at the gathering in Canada, Mr Trump rated his relationship with their leaders as a “10” - naming Germany’s Angela Merkel, French President Emmanuel Macron and Mr Trudeau, but not the UK Prime Minister.
As well as criticising the tariffs, Mrs May also opposed Mr Trump’s call for Russia to be readmitted to the group of leading industrialised nations.
But Mr Trump insisted it would be an “asset” to have Vladimir Putin back at the summit table.
The US president, who left the summit in La Malbaie early to head for his talks with North Korean leader Kim Jong Un, told reporters the US needed protectionist tariffs because “we are like the piggy bank that everyone is robbing”.
Mr Trump warned the EU: “If they retaliate they are making a mistake.”
Mrs May said: “Where we disagree with our allies on something it is right that we say so and air the issue openly and frankly.
“We have done just that at this summit, registering our deep disappointment at the unjustified decision by the US to apply tariffs to EU steel and aluminium imports.
“In response, the EU will impose counter-measures.”
• READ MORE: Acrimonious start to G7 summit after Trump tweets
But “at the same time we need to avoid tit-for-tat escalation” and maintain a constructive dialogue, she said.
The Prime Minister said the UK still wanted to discuss a post-Brexit trade deal with the US and said Mr Trump was still looking forward to July’s visit to Britain.
“We have a very good relationship with President Trump, we work with President Trump, the UK has a very good relationship with the US,” she said.
“President Trump and I had a brief word here at the summit about how he is looking forward to his visit to the UK and I look forward to welcoming him to the UK.”
The US president repeated his call for Vladimir Putin to join the other leaders around the summit table.
“I think it would be an asset to have Russia back in, I think it would be good for the world, I think it would be good for Russia, I think it would be good for the United States, I think it would be good for all the countries of the current G7,” he said.
“I think the G8 would be better, I think having Russia back in would be a positive thing.”
Russia was thrown out of the group in 2014 over the annexation of Crimea.
Mrs May has been at the forefront of diplomatic efforts to build an alliance against Russia after the Salisbury nerve agent attack on ex-spy Sergei Skripal and his daughter Yulia.
She said: “If there are to be any conversations about Russia’s future in relation to this particular group, they have to change their ways, they have to change the route that they are taking and the sort of activity they are involved in.”
Mr Trump’s strained relationship with the rest of the G7 was in evidence on Saturday when he arrived late for the opening session, with Mr Trudeau addressing a gathering that included an empty chair where the president was meant to be.
But despite the rows over trade and Russia, Mr Trump rated his relationship with other G7 leaders as 10 out of 10.
“I would say that the level of relationships is a 10 - we have a great relationship. Angela (Merkel) and Emmanuel (Macron) and Justin (Trudeau) - I would say the relationship is a 10.
“The relationship that I’ve had with the leaders of these countries - I would really rate it, on a scale of zero to 10, I would rate it a 10.
“That doesn’t mean I agree with what they are doing, and they know very well that I don’t.”