Donald Trump accused the European Union of a “brutal” approach to trade with the United States and warned that retaliating to American steel tariffs would be a mistake.

The US president accused other states of “robbing” his country through their trade policies.

Despite being at odds with other countries 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 Canada’s Justin Trudeau, but not the UK’s Prime Minister.

Theresa May and Justin TrudeauPrime Minister Theresa May meets Canadian PM Justin Trudeau at the G7 summit (David Hughes/PA)

Theresa May has criticised the tariffs and also opposes 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 has slapped a 25% tariff on imports of steel and 10% on aluminium from countries including the UK and the rest of the European Union.

In response, the EU is preparing new tariffs set to hit US exports ranging from jeans to bourbon whiskey.

Mr Trump, who was leaving the summit in La Malbaie early, told reporters the US needed protectionist tariffs because “we are like the piggy bank that everyone is robbing”.

Mrs May pleaded with fellow leaders to step back from the brink of a damaging trade war at a session of the summit on Friday night.

The UK is thought to have concerns about the European Commission’s proposed package of 2.8 billion euro (£2.46 billion) of tariffs on US goods.

Mr Trump said: “If they retaliate they are making a mistake.”

The US president also repeated his call for Vladimir Putin to join the other leaders around the summit table.

“Some people like the idea of bringing Russia back in. This used to be the G8 and not the G7 and something happened a while ago where Russia is no longer in,” he said.

“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.

“I think the G8 would be better, I think having Russia back in would be a positive thing.

“We are looking for peace in the world, we are not looking to play games.”

Russia was thrown out of the group in 2014 over the annexation of Crimea.

The Prime Minister 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 that “before any such conversations can take place” about readmitting Russia, the Kremlin “needs to change its approach”.

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.”

Theresa MayMrs May is against Russia rejoining the elite group (Simon Dawson/PA)

Because of the divisions, it was unclear whether the gathering would be able to secure a joint communique agreed by all leaders setting out what had been achieved at the summit – something that has not happened since 2007.

Instead, a chairman’s statement from the host Mr Trudeau could be produced, setting out what was discussed and where agreement had been impossible.

A senior UK Government source said: “What matters is getting the substance right. At previous meetings this has been done in a number of ways, such as a chairman’s statement.”