As uncertainty around US military support for Europe grows, European leaders have started to mull how to address the continent's lack of a credible deterrent.

Last week, the European Union's foreign policy chief Kaja Kallas told Finnish newspaper Helsingin Sanomat that a discussion should be initiated on developing Europe's own nuclear deterrent.

France and Britain are currently the only European nations with nuclear arsenals.

Speaking to AFP, Finland's defence minister Antti Hakkanen stressed that the US remains committed to maintaining nuclear deterrence within NATO.

"We fully trust ... that the US is fully committed to the nuclear deterrence in NATO," he said, adding that European countries were "taking the leading role in conventional defence".

But Hakkanen welcomed the discussion on a "stronger European nuclear deterrence".

"If there's going to be some kind of bigger European investments in France or UK's nuclear deterrence, that's only a good thing," Hakkanen said, but stressed that Europe was not yet capable of matching US capabilities.

"If you're talking about to compensate US nuclear deterrence, that's not realistic at this point," he added.

Last week, the New START treaty which restricted the US and Russia to 1,550 deployed nuclear warheads each expired, marking the first time in decades without a treaty to curtail the positioning of the planet's most destructive weapons and sparking fears of another arms race.

The treaty's expiration also marks an end to major bilateral nuclear-disarmament accords and a potential shift towards a looser nuclear order, profoundly reshaped by China's growing diplomatic and technological prowess.

NATO chief Mark Rutte late January warned that Europe cannot defend itself without the US after tensions over Greenland prompted calls for the continent to stand on its own feet.

"If anyone thinks here again, that the European Union, or Europe as a whole, can defend itself without the US -- keep on dreaming. You can't," Rutte told lawmakers at the European Parliament.