BRUSSELS (AFP) - European Commission chief Jean-Claude Juncker said Tuesday (Nov 15) he was worried about Donald Trump's approach to EU-US ties given what the president-elect said during a "disgusting" election campaign.

"It worries me in as much as I have difficulty imagining - or perhaps I should imagine - that the new president-elect of the United States will put into practice everything that he said during an electoral campaign that I found absolutely disgusting," Juncker told Belgian RTL radio.

"It was not American democracy's hour of glory."

Trump's upset victory badly rattled nerves in Europe after he appeared to call into question Washington's near 70-year security guarantee by saying he would only help Nato allies if they paid their way.

EU allies have also been alarmed by Trump's apparent closeness to Russian President Vladimir Putin at a time when relations between Moscow and Brussels are strained over the conflicts in Ukraine and Syria.

"I wonder about Trump's real intentions with the Atlantic alliance," added Juncker, who heads the executive branch of the 28-nation European Union.

"I wonder about the trade policies that he will bring in, and this temptation he has to turn towards total isolationism (which) would be in the interest of neither the United States nor Europe."

His comments came just days after former Luxembourg prime minister Juncker said Trump must get up to speed on how Europe works in order to avoid "two years of wasted time" when he assumes his new role.