US President Donald Trump blindsided Kyiv and its European backers this week by launching talks on ending Moscow's three-year invasion in a call with Russia's Vladimir Putin.

The new US administration has also warned its NATO allies that Washington will no longer be primarily focused on the continent's security and may have to shift forces elsewhere to focus on China.

The Kremlin has pushed for the negotiations -- set to kick off in Saudi Arabia in the coming days -- to discuss not just Ukraine but also broader European security.

That has sparked fears among Washington's allies that Putin could return to demands he floated prior to the 2022 invasion aimed at limiting NATO's forces in eastern Europe and US involvement on the continent.

One issue talks "should not discuss is new European security arrangements", Stubb, whose country shares a 1,300-kilometre border with Russia, told the Munich Security Conference.

"There's no way in which we should open the door for this Russian fantasy of a new, indivisible security order, where it can do spheres of interest."

The stance from the new US administration has sown further concerns in Europe as Trump demands NATO countries spend more on their own defence.

Pentagon chief Pete Hegseth this week warned that Washington will no longer be primarily focused on the continent's security and may have to shift forces elsewhere to focus on China.

Stubb insisted that Ukraine's push to join NATO and the European Union should be "non-negotiable", even after Washington appeared to rule out Kyiv joining the military alliance as part of a peace deal.

Stubb laid out a vision for how negotiations could work -- saying that the West should hit Russia with tough sanctions ahead of talks to pile on the pressure.

He said European countries should help support any eventual ceasefire, with the United States acting as a "backstop".