Russian President Vladimir Putin and German Chancellor Angela Merkel discussed the Ukraine crisis in a telephone call and stressed the importance of "effective international action" to reduce tension, the Kremlin has said.
During their discussion on Sunday, the leaders also discussed the supply of Russian gas and its transit, based on the results of a recent meeting in Warsaw.
In Warsaw on Friday, Russia threatened to cut natural gas supplies to Ukraine in June if it receives no prepayment in an escalating row between Moscow, Ukraine and the European Union over energy supplies.
Also on Friday, Merkel and U.S. President Barack Obama warned Russia it would face additional sanctions against key sectors of its economy if Moscow interferes with Ukraine's elections on May 25.
Obama and Merkel said they were united in their intention to implement tougher sanctions but made clear they were still deciding how to structure the measures should they be necessary.