BRUSSELS (AFP) - EU ministers approved a common defence plan on Monday despite sharp differences over how far it should go, as Donald Trump's election win stoked fears about Washington's commitment to European security.

Trump's campaign threat to think twice about defending NATO allies unless they up their defence spending has driven calls for the European Union to press ahead on its own, despite objections from Britain.

EU foreign policy chief Federica Mogherini insisted the plans - to boost the bloc's ability to respond to external conflicts, help partner countries build their defence capabilities and protect EU citizens - would not undermine NATO.

"It's not about a European army, it's not about creating a new European Union-style headquarters," Mogherini said after talks with foreign and defence ministers in Brussels, referring to NATO's own military HQ.

Britain has long opposed any such moves as undermining NATO, but after its shock June Brexit vote, France and Germany jumped in with plans to boost defence cooperation that have now gained extra urgency with Trump's election victory.

Mogerhini said the bloc was working on the issue long before the US vote and that it would "continue to do this in strong partnership with NATO".

The meeting's final statement made no mention of a possible EU military headquarters in Brussels, but said they had asked the bloc's foreign policy service to develop a "permanent" system for coordinating civilian-military measures.

The issue exposed a rift between the bloc's two biggest military powers, France and Britain, which is set to leave the EU in two years after the Brexit vote in June.

French Foreign Minister Jean-Marc Ayrault said the defence plan was an "essential step forward" for Europe to show it can take defence decisions on its own in an "increasingly uncertain world".

But British Defence Secretary Michael Fallon meanwhile bluntly told the EU to stop "dreaming".

"Instead of planning expensive new headquarters or dreaming of a European army, what Europe needs to do now is to spend more on its own defence, that is the best possible approach to the Trump Presidency," Fallon said.

British foreign secretary Boris Johnson, a leading Brexit supporter, said earlier that Trump's election offered a "moment of opportunity" and the EU should wait to see what he wanted.

"Donald Trump, as I've said before, is a dealmaker," he said, warning: "You shouldn't undermine the fundamental security architecture that's looked after us for the last 70 years." Johnson had snubbed special talks on Trump's election hosted by Mogherini over dinner on Sunday, saying the meeting risked sending the wrong message to the new president.

Mogherini insisted after Sunday's session that ministers backed a "very strong partnership" with Trump, but that the EU would have to move on with its own plans nonetheless.

The EU has no military arm but has mounted a series of combined civilian and military operations such as in central Africa or to combat piracy off the Horn of Africa.

EU diplomats say Brexit and now Trump's election have put defence firmly on the agenda.

Nuclear-armed Britain counts as the bloc's most powerful military power and the United States through NATO has guaranteed Europe's security since 1949.

They also say that while Britain has been most opposed to a larger military role, other member states - of which 22 of the EU's 28 also belong to NATO - are now being forced to come forward with their reservations.

For example, Poland and the Baltic states want Trump to stick by commitments to increase NATO's eastern presence so as to deter a more aggressive Russia.

The election over the weekend of Moscow-friendly presidents in Moldova and EU member Bulgaria will likely heighten concerns on that front.