President Trump's tone has shifted both toward Putin and regarding the continuation of U.S. military support for Ukraine.

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,

U.S. President Donald Trump's decision to ramp up arms shipments to Ukraine is a signal to Kyiv to abandon peace efforts, Russia said on Thursday, vowing it would not accept the "blackmail" of Washington's new sanctions ultimatum.