US President Donald Trump has turbocharged calls for Europe to rearm by casting doubt on Washington's central role in NATO and making overtures towards Russia on Ukraine.

In a bid to give the EU's 27 countries the tools to ramp up spending, Brussels this month unveiled a raft of proposals it says could mobilise up to 800 billion euros ($875 billion).

On Wednesday, the bloc's foreign and defence chiefs put flesh on the bones of those plans, setting a timeline -- starting from next month -- for member states to react.

"This is a pivotal moment for European security. It is a pivotal moment for action," foreign affairs chief Kaja Kallas said.

The plan proposes easing the bloc's fiscal rules to allow states to spend much more on defence, a measure the commission says could potentially unlock 650 billion euros over four years.

In a white paper unveiled Wednesday, Brussels urged EU countries to kick off that process by April.

It also said they should approve "as a matter of urgency" an initiative to provide member states with up to 150 billion euros in loans backed by the EU's central budget.

But the paper steered clear of recommending a bigger programme of joint borrowing, despite some EU countries arguing that the bloc needs the same massive infusion of cash it pumped in to recover from the Covid pandemic.

"Right now, it's not there," Kallas said.

"But is it completely off the table? I don't think so," she added, saying it could still be envisioned to finance flagship common projects between countries.

- 'No big bang' -

Bolstering Europe's defences is to top the agenda at an EU leaders' summit later this week, the third time in six weeks they will have urgently addressed the subject.

"450 million EU citizens should not have to depend on 340 million Americans to defend ourselves against 140 million Russians who can't defeat 38 million Ukrainians," EU defence commissioner Andrius Kubilius said.

"We really can do better. It's time for us to take responsibility for the defence of Europe."

The proposals from Brussels are just a part of efforts being put into action by governments as they come to terms with the realisation the United States may no longer have their backs.

The likes of Poland and the Baltic states have already ramped up their spending well beyond the NATO threshold of two percent of GDP.

Lawmakers in economic heavyweight Germany on Tuesday took the seismic move of voting for a colossal defence and infrastructure spending package proposed by chancellor-in-waiting Friedrich Merz.

One EU diplomat said the white paper captured the "threat and urgency" of the challenge facing the bloc, but did not go far enough on ways to boost funding.

"All in all there is no big bang," the diplomat said.

A key part of the EU's proposals is not just to equip its forces to face the menace from Russia but also to make sure investments bolster European defence firms.

Brussels said at least 65 percent of the cost of the weapons bought under the 150-billion-euro programme should be spent in the EU, Norway or Ukraine.

The door appeared open for Turkey to be part any joint procurement scheme, but Britain would have to sign a security deal with the EU if it wants to come in on the project.