U.S. President Joe Biden's agreement in principle to meet President Vladimir Putin may be off after Russia declared two breakaway regions of Ukraine as independent on Monday, and the United States will announce further measures, likely sanctions-related, on Tuesday, a senior administration official said.
The official, speaking to reporters on a conference call, said the United States would continue to pursue diplomacy with Moscow over Ukraine "until the tanks roll."
(Reporting by Jeff Mason and Idrees Ali)
