European Commission President Jean-Claude Juncker says U.S. President Donald Trump invites conflict by undermining the EU | John Thys/AFP via Getty Images Juncker says Trump’s anti-EU talk could lead to new Balkan war Commission president warns US president not to encourage countries to follow the UK’s lead and leave the bloc.

Donald Trump's calls for countries to copy Brexit could lead to another war in the Balkans, European Commission President Jean-Claude Juncker said in an interview published Friday.

Speaking to the Financial Times, Juncker said the U.S. president's enthusiasm for Brexit was “annoying” and “surprising.”

The former Luxembourg prime minister said he had delivered a warning for Trump to his vice president, Mike Pence, when he visited Brussels last month. “I told the vice president, ‘Do not say that, do not invite others to leave, because if the European Union collapses, you will have a new war in the Western Balkans,'” Juncker said.

He said it was important for countries in the Western Balkans to have the prospect of EU membership, "If we leave them alone — Bosnia Herzegovina, Republika Srpska, Macedonia, Albania, all those countries — we will have war again.”

The Commission president also said Trump's "America First" rhetoric was frightening Europeans and added that for the first time in postwar history, a U.S. president was giving the impression that he was not interested in European affairs.

Juncker is planning to go to Washington next month, but a meeting with Trump hasn't been confirmed. "They’re trying to fix it, but he has other priorities. By the way, he does not understand anything about Europe,” Juncker said. “He had [European Council President Donald] Tusk on the phone and he thought it was me.”

As for Brexit, Juncker said Brussels had calculated the U.K.'s Brexit bill at up to €60 billion. In an interview with BBC, aired Friday, Juncker said the EU will negotiate the U.K.’s exit in a "friendly” and “fair” way.