Helsinki: On the eve of his meeting with Russia's Vladimir Putin, US President Donald Trump has rattled allies once more by labelling the European Union a "foe" with regard to trade.

In a pre-summit interview with CBS News' Face the Nation program aired on Sunday, Trump lumped the EU with China and Russia as US economic adversaries. "I think the European Union is a foe, what they do to us in trade," he said.

President Donald Trump arrived in Finland on Sunday for a closely watched one-on-one summit with Russian President Vladimir Putin, hours after telling an interviewer that he was going into the meeting on Monday with "low expectations."

Donald Tusk, president of the European Council, replied on Twitter using one of Trump's favourite stock phrases.