UN Security Council members held a heated debate Wednesday over reports of North Korean troops being sent to Russia.

The council called an emergency meeting at Ukraine’s request.

Ukraine’s ambassador to the UN, Sergiy Kyslytsya, said up to 12,000 North Koreans are being trained at five locations in Russia’s Eastern Military District.

He also said that between October 23 and 28, at least seven planes carrying up to 2,100 troops flew toward Russia’s border with Ukraine. He added that in November North Korean military personnel “are expected to begin directly participating in combat operations against the Ukrainian defense forces.”

Council members expressed concern about these developments.

Japan’s ambassador Yamazaki Kazuyuki said: “North Korea becoming complicit in Russia’s unprovoked aggression will worsen the situation in Ukraine.”

Russian Ambassador Vassily Nebenzia responded that Russia’s interaction with North Korea on military and other issues is in line with international law and that no one can prohibit it.

North Korean Ambassador Kim Song did not directly address the reports of troops in Ukraine. But he said that “if Russia’s sovereignty and security interests are exposed and threatened by continued dangerous attempts by the United States and the West, and if we are deemed to respond,” then his country will make “a necessary decision.”

US Deputy Ambassador Robert Wood said that “these destabilizing activities are a major threat to peace and security, not only in Europe, but in the Indo-Pacific.”

He added that if North Korean troops enter Ukraine in support of Russia, “they will surely return in body bags.”

Wood said he would advise North Korean leader Kim Jong Un to “think twice before engaging in such reckless and dangerous behavior.”