A tripartite meeting between U.S., Finnish and Swedish defense officials convened on Tuesday in Helsinki, and Finnish Defense Minister Jussi Niinistö said the next tripartite meeting would take place next spring.

Tuesday's meeting, gathering Niinistö, U.S. Defense Secretary James Mattis and Swedish Defense Minister Peter Hultqvist, was the first of its kind between the three countries at ministerial level. Analysts believed it would signal closer defense cooperation between the U.S. and the two Nordics.

Niinistö said the three-party meetings would not replace bilateral U.S.-Finland cooperative institutions. Niinisto said the new type of meetings is practically useful for the U.S. as Finland and Sweden are both in the EU but outside NATO. "It is useful to speak with both at the same time."

Concluding his visit to Finland, Mattis said on Tuesday the U.S. and Finland had "shared appreciation of the security situation" in Northern Europe. Mattis praised the Finnish defense forces not only for their tactical abilities but also for their ethics.

Asked to elaborate on the ethics issues, Niinistö said it referred to the experience from Finnish forces in peace keeping operations over the years.

On Tuesday, Niinistö invited the U.S. to participate in an envisioned major military exercise in Finland in 2020. Niinisto said it was not an official invitation as a final decision on the exercise had not been taken.

The aim of the would-be exercise in Finland has been described as "training for being able to receive assistance from foreign forces". Mattis gave no direct answer to the Finnish request, but Finnish national broadcaster Yle quoted sources as saying the U.S. would be taking part as long as schedule is suitable.

Niinistö gave no answer when asked whether the U.S. would be allowed to use Patriot missiles in Finland or not.

The 2020 plan was also discussed in the NATO Northern Group meeting on Tuesday. Niinistö told media, however, that acceptance of European participation would also depend on what kind of input would be offered. "We cannot take everything," he said.