Joe Biden has announced the first wave of sanctions against Russia in response to Moscow’s actions in Ukraine.
The US president said Russian troop deployments in eastern Ukraine marked the “beginning of an invasion”.
He warned Moscow that it would “pay an even steeper price if it continues its aggression”.
The sanctions target Russian banks and sovereign debt.
Mr Biden also said he had authorised the movement of additional forces and equipment to bolster Baltic states in response to Russia’s activity in eastern Ukraine.
“We will defend every inch of NATO territory,” he said.
In a fast-moving crisis, Russian legislators earlier gave President Vladimir Putin permission to use armed forces abroad.
Moscow recognised the independence of Russian-backed rebel regions in eastern Ukraine on Monday.
Ukraine key developments:
- UK targets five Russian banks and three oligarchs with sanctions
- EU sanctions Russian MPs who voted in favour of recognition
- White House refers to Russian troop deployments as an ‘invasion’
- Ukrainian president considering breaking off diplomatic ties with Russia
- Germany halts approval of Nord Stream 2 gas pipeline