Updated

The German government says Chancellor Angela Merkel has proposed to Russian President Vladimir Putin that an international observer mission in Ukraine be expanded quickly as tensions rise in the country's east.

Merkel spokesman Steffen Seibert said in a statement the two leaders discussed the situation in Ukraine by phone Sunday "notwithstanding their differing views" on Crimea's disputed referendum on whether to seek to join Russia.

Merkel criticized Russian forces for taking control of a natural gas distribution station in Ukraine just outside Crimea on Saturday.

Seibert says Merkel proposed quickly expanding the 57-nation Organization for Security and Cooperation in Europe's presence in Ukraine, and urged a decision at an OSCE meeting Monday on sending more observers to tense areas particularly in eastern Ukraine. He says Putin "evaluated this initiative positively."