Obama threatens more sanctions against Russia

President Barack Obama on Thursday urged European and other allies to be prepared to join U.S. in imposing additional sanctions on Russia if it "escalates the crisis in Ukraine."

In a phone conversation with German Chancellor Angela Merkel, Obama expressed "concerns" over situation in eastern Ukraine, where "separatists apparently with support from Moscow continue an orchestrated campaign of incitement and sabotage to destabilize Ukraine."

The pair also repeated the call for Russia to move its troops back from the border region.

They also discussed issues about the upcoming meeting of the Ukrainian, Russian, and U.S. foreign ministers and EU High Representative, according to a White House statement.

The United States has accused Russian agents of stirring unrest in eastern Ukraine to use it as a pretext for military intervention. Russia has rejected such an accusation.