The top U.S. negotiator in nuclear arms control talks with Russia held in Helsinki says a one-day follow-up meeting to earlier talks in Austria has yielded ``important progress.''

Ambassador Marshall Billingslea, President Donald Trump's special envoy for arms control, gave the upbeat view in a tweet Tuesday, a day after the talks in the Finnish capital with Russian Deputy Foreign Minister Sergei Ryabkov. He gave no further detail.

The low-profile negotiations were meant as an update to a U.S.-Russia dialogue on nuclear arms in Vienna in June, July and August.

Monday's talks are thought to have focused on producing a new agreement to replace, or to extend, the New START treaty that expires in February _ the last remaining pact constraining the arsenals of the world's two major nuclear powers.

In Moscow, the tone was much more skeptical. Speaking at a meeting with European business leaders on Monday, Russian Foreign Minister Sergey Lavrov accused Washington of ``unilateralism'' and said the New START treaty would likely cease to exist.

Lavorov said the conditions for the treaty's extension that the U.S. has put forward are ``absolutely unilateral and don't take into account our interests, or the experience of many decades when arms control has existed to mutual satisfaction.''

After Monday's talks, Billingslea and Ryabkov met separately with Finnish President Sauli Niinisto who said that ``in the current world situation all dialogue is important, and I welcome its continuation between the United States and Russia.''

Finland, a militarily non-aligned European Union nation that isn't a NATO member, has a long legacy going back to the Cold War era of hosting U.S.-Russian summits and acting as a neutral ground for negotiations between officials from Washington and Moscow.

Trump and Russian President Vladimir Putin held their first dedicated summit in Helsinki in July 2018.