Russian President Vladimir Putin says the growing crisis in Ukraine has brought the country to the brink of civil war.
The Kremlin says Mr. Putin made his comment during a telephone call Tuesday with German Chancellor Angela Merkel.
President Putin accused the Ukrainian government of pursuing an "anti-constitutional" path by using force against the pro-Russian demonstrators who have taken over official buildings in 10 southeastern Ukrainian towns and cities.
The Kremlin says the Russian and German leaders hope Thursday's talks in Geneva between the European Union, Russia, Ukraine, and the United States will show the importance of finding a peaceful solution.
Meanwhile, witnesses in the Ukrainian city Sloviansk near the Russian border say six armored personnel carriers flying the Russian flag have rolled into the town.
A number of armed men sat on top of the vehicles, waving to the people in the streets.
Also, armed pro-Russians have taken over the mayor's office and the city council building in Donetsk.
Ukraine launched what it calls an anti-terrorist operation in Sloviansk and other towns Tuesday to try to take back the government buildings seized by the protesters.
There are different reports on whether shots were fired, if there are any casualties, and who controls what.
The protesters are demanding referendums on whether the cities will split from Ukraine and join Russia. A similar vote in last month in Crimea led to the Russian takeover of the Ukrainian peninsula.
Moscow says it has the right to protect Russian-speakers in Ukraine.