Updated

German Chancellor Angela Merkel has called Russia's President Vladimir Putin to discuss the situation in Ukraine.

Merkel's office said she and Putin had "different assessments of events" in Ukraine during their telephone conversation late Tuesday.

It said the conversation focused on preparations for a planned meeting of senior diplomats from Russia, Ukraine, the United States and the European Union in Geneva on Thursday.

Earlier Tuesday Ukrainian forces clashed with armed gunmen at a small airport after the country's acting president, Oleksandr Turchynov, announced an "anti-terrorist operation" against the armed, pro-Russian insurgents who had seized control of numerous buildings in the eastern part of the country.