BRUSSELS — The secretary-general of NATO, Jens Stoltenberg, says the military organization is setting up new multinational battlegroups in eastern Europe to deter Russia from launching an attack on any of its members.

The battlegroups, which usually number between 1,000-1,500 troops, will be set up in Hungary, Slovakia, Romania, and Bulgaria. Mr. Stoltenberg says they will remain in place “as long as necessary.”

Speaking Wednesday on the eve of a summit of NATO leaders, Mr. Stoltenberg said that Russia’s war on Ukraine means “a new normal for our security and NATO has to respond to that new reality.”

Mr. Stoltenberg says the leaders are likely to agree to send more assistance to Ukraine, including “equipment to help Ukraine protect against chemical, biological, radiological and nuclear threats.”

NATO’s 30 allies are worried about Russian rhetoric and fears that Moscow might want to create a pretext to use chemical weapons in Ukraine.

Mr. Stoltenberg says that “any use of chemical weapons would totally change the nature of the conflict,” and would have “far-reaching consequences” for Russia. He declined to elaborate.