Russia's nuclear rules say it can use atomic weapons if the country — or one of its allies — is attacked, especially if the attacker is a non-nuclear nation backed by a nuclear power. That clause could be seen as applying to Ukraine,

The Kremlin said U.S. President Donald Trump signaled to Ukraine that it should continue the war after he said he would send more weapons to Kyiv and threatened Russia with secondary sanctions unless it makes peace.

Trump said the United States would put secondary tariffs on countries that do business with Russia if a peace deal is not reached in 50 days.