By Tom Balmforth, Polina Nikolskaya and Jarrett Renshaw

MOSCOW/DONETSK/WASHINGTON: U.S. President Joe Biden announced on Tuesday new sanctions in retaliation for Russia recognising two breakaway regions of Ukraine and sending troops there, adding to Western efforts to stop what they fear is the beginning of a full-scale invasion.

The measures target Russian banks and sovereign debt, among other steps.

One of the worst security crises in Europe in decades is unfolding as Russian President Vladimir Putin authorised sending what he calls peacekeping troops to separatist areas of Donetsk and Luhansk after recognising them as independent.

Weeks of intense diplomacy have so far failed as Moscow calls for security guarantees, including a promise that its neighbour Ukraine will never join NATO, while the United States and its allies offer Putin confidence-building and arms control steps.

"He's setting up a rationale to take more territory by force," Biden said at the White House.

"I'm going to begin to impose sanctions in response, far beyond the steps we and our allies and partners implemented in 2014," he added, in a reference to Russia's annexation of Crimea from Ukraine.