NATO doubles its battlegroups in Eastern Europe ahead of multiple summits.

BRUSSELS — NATO is doubling its battlegroups on the alliance’s eastern flank in response to Russia’s continuing war in Ukraine, the group’s secretary general said on Wednesday before a major summit in which President Biden will meet with European allies in Brussels in the coming days.

The secretary general, Jens Stoltenberg, also focused on what import Russia’s potential use of any chemical or biological weapons in Ukraine could hold for NATO, saying that such use would “fundamentally change the nature of the conflict.” And he upped the rhetoric on China’s role in bringing the conflict to an end, cautioning Beijing not to provide material support to Moscow.

Mr. Stoltenberg’s remarks, in a news briefing one day before the start of an unusual series of back-to-back summits over Russia’s brutal monthlong invasion of Ukraine, which shows no sign of ending.

“The first step is the deployment of four new NATO battlegroups in Bulgaria, Hungary, Romania and Slovakia, along with our existing forces in the Baltic countries and Poland,” he said, detailing the bolstering of NATO’s posture along its eastern frontier. “This means that we will have eight multinational NATO battlegroups all along the eastern flank, from the Baltic to the Black Sea,” he added.

“All of this is the immediate response to the Russian invasion of Ukraine,” Mr. Stoltenberg said, adding that the forces would remain there “as long as necessary.”

NATO leaders will convene in Brussels on Thursday for a summit focusing on the invasion. Mr. Biden will then join E.U. leaders on Thursday afternoon in Brussels — the Belgian capital, which hosts both the NATO and European Union headquarters — in a second summit. And leaders from the Group of 7 leading world economies, which include the United States and several E.U. countries as well as Canada, will gather on Thursday evening to discuss the Ukraine crisis.

President Volodymyr Zelensky of Ukraine will join that last summit via videoconference, an E.U. official said.

In his news briefing, Mr. Stoltenberg said that any use of chemical or biological weapons — which are banned by treaty — by Russia in Ukraine would be “a blatant violation of international law.”

The use of such weapons would have “severe consequences,” he said, leading not only to possible devastation inside Ukraine, but also “severe consequences for neighboring countries because of the contamination or spread of chemical agents for biological agents will of course also potentially affect neighbors.”

Mr. Stoltenberg maintained that the alliance was eager to avert a direct confrontation with Russia and would therefore not deploy NATO troops in Ukraine or respond to Ukrainian pleas for a NATO-enforced no-fly zone.

At the same time, he cautioned China against worsening the conflict by providing material support to Moscow.

“Beijing has joined Moscow in questioning the right of independent nations to choose their own path,” Mr. Stoltenberg said, using more pointed language toward China than he has previously.

“China has provided Russia with political support, including by spreading blatant lies and misinformation,” Mr. Stoltenberg said. “And allies are concerned that China could provide material support for the Russian invasion.”