Russia has told the US that Western sanctions over the Crimea dispute are unacceptable, and has threatened “consequences”.
Russian Foreign Minister Sergei Lavrov issued the warning in a telephone call to US Secretary of State John Kerry.
It came hours after Russian and Crimean leaders signed a treaty absorbing the peninsula into the Russian Federation.
Crimean voters chose to secede from Ukraine in a disputed referendum on Sunday.
On Monday, the US and the EU imposed sanctions on several officials from Russia and Ukraine accused of involvement in Moscow’s actions in the Black Sea peninsula.
After the signing of the treaty on Tuesday, the White House said those sanctions would be expanded.
US Vice-President Joe Biden accused Russia of a “land grab”.
After Lavrov spoke to Kerry, the Russian foreign ministry said in a statement: “(Crimea) republic residents made their democratic choice in line with the international law and the UN charter, which Russia accepts and respects.
“The sanctions introduced by the United States and the European Union are unacceptable and will not remain without consequences.”
It did not spell out what those consequences might be.
Kerry later warned that any incursion by Russia into eastern Ukraine would be “as egregious as any step I can think of”.
“I hope we don’t get there,” he added.