RAMSTEIN AIR BASE, Germany: The White House says President Barack Obama and German Chancellor Angela Merkel have spoken about their concern over the "significant increase in violence" in eastern Ukraine.

The leaders spoke by phone on Tuesday as Obama traveled back to the U.S. from a trip to India and Saudi Arabia. Air Force One stopped briefly at a U.S. base in Germany to refuel.

The White House says Obama and Merkel agreed on the need to hold Russia accountable for its support for the separatists and failure to fulfill its commitments under a peace agreement. And they discussed the importance of finalizing a "robust package of financial support" for Ukraine.

In recent weeks, the separatists have launched a series of new offensives along the Russian border.