European Union countries have been pushing to ramp up their defence sectors in the face of Russia's invasion of Ukraine, but there was no clarity on how to raise the sums needed.

EU chief Ursula von der Leyen said in June the bloc needs to invest 500 billion euros ($535 billion) in the next decade to boost its defences.

The options being mooted include issuing EU defence bonds -- a joint borrowing scheme, similar to how the bloc financed its recovery programme after the Covid pandemic.

"I think this is the first time... that the five largest countries in the European Union have come out in favour of European defence bonds," Sikorski said after hosting talks with counterparts from France, Germany, Italy and Spain, as well as Britain.

The 27-member EU also tapped former Lithuanian prime minister Andrius Kubilius for a new defence commissioner role tasked with leading this push.

Kubilius in September urged "new bold steps" to raise the huge sums for defence.

Echoing his call, Sikorski said the commissioner "must be given serious resources to carry out a serious mission".