An army would allow the EU to react in a "credible manner" to threats to peace in a member state or in a neighbouring country, he noted.

"You would not create a European army to use it immediately," said Juncker, who was previously prime minister of Luxembourg. "But a common European army would send a clear message to Russia that we are serious about defending European values."

Juncker added that a European army would not be "competition" for Nato, to which 22 of the 28 EU states belong, but about strengthening Europe.

"A European army would show the world that there will never again be war between its member states."

The idea of a common EU army has been floated on and off for many years but has always run into opposition, particularly in Britain, one of the two member states (along with France) that is considered to be a major defence player.

It reiterated its opposition once again on Sunday.

“Our position is crystal clear that defence is a national – not an EU – responsibility and that there is no prospect of that position changing and no prospect of a European army," a government spokesperson said, according to the Guardian.

The EU army idea has never gained real traction across member states for an array of reasons, with objections on grounds of ideology, politics, culture and tradition.

Joint EU missions abroad - such as the border assistance mission in Libya - have been common for 10 years, but when France in 2013 wanted military action in Mali to counter a jihadist threat, it did it alone.

Meanwhile the EU's battlegroups, meant to be deployed rapidly in a military crisis, have never been used.

Juncker's words did receive a cautious welcome by Germany's defence minister, however.

Ursula Von der Leyen told German radio that she believed that the German army could "under certain circumstances" be prepared to put soldiers under the control of another nation. Such a move would “strengthen Europe’s security” and “strengthen a European pillar in the transatlantic alliance”.

She said "our future as Europeans will one day be a European army" although she added "not in the short term".

Juncker's words on an EU army and the state of EU foreign policy come as the EU has begun to assess how it deals with its near-abroad.

Last week the European Commission suggested that its neighbourhood policy - a soft policy focussing on trade access in return for raising democratic standards - had been "inadequate" in dealing with the Arab Spring and former Soviet countries.

Meanwhile, Russia's annexation last year of Crimea as well as its ongoing involvement in fighting in eastern Ukraine has also exposed the limits of EU foreign policy.

The EU has agreed several rounds of sanctions against Moscow, but it remains internally divided on how hard it should be on Russia.