Five Nordic nations agreed on the expansion of military cooperation and increased solidarity with the Baltic states on Thursday, citing threats from Russia as the biggest challenge to European security.

In a joint declaration, the heads of the defense ministries of Sweden, Norway, Finland, Denmark and Iceland said that Europe must prepare for possible crisis situations caused by Russia, Reuters reported, citing the Norwegian Aftenposten newspaper. The five northern European countries are expected to expand joint military exercises and strengthen cooperation in the sphere of defense and intelligence information sharing.

“Russia's leaders have shown that they are prepared to make practical and effective use of military means in order to reach their political goals, even when this involves violating principles of international law,” the defense ministers wrote in the statement.

“There is increasing military and intelligence activity in the Baltics and in our northern areas. … The Russian military is challenging us along our borders and there have been several border infringements in the Baltics,” the ministers added.

Although Finland and Sweden are not members of NATO, they have significant cooperation with the intergovernmental military alliance, Reuters reported, adding that the joint statement is one of their strongest responses to the so-called Russian aggression.

“Russia's actions are the biggest challenge to the European security,” the ministers said in the statement. “Russia’s propaganda and political maneuvering are contributing to sowing discord between nations, and inside organizations like NATO and the EU.”

The joint statement from the Nordic nations has come as the former Polish President Lech Walesa told a Ukrainian magazine that the West should use its arsenal of nuclear weapons to confront Russian President Vladimir Putin.

To curb Russian aggression, the West should consider “sending in nuclear missiles,” Sputnik quoted Walesa as saying. “It’s important to show we have them, and that they are better than Russia’s.”