DONETSK, Ukraine (AP) - Pro-Moscow activists barricaded inside government buildings in eastern Ukraine proclaimed their regions independent Monday and called for a referendum on seceding from Ukraine - an ominous echo of the events that led to Russia's annexation of Crimea.
The Ukrainian government accused Russia of stirring up the unrest and tried to flush the assailants from some of the seized buildings, setting off fiery clashes in one city. Russia, which has tens of thousands of troops massed along the border, sternly warned Ukraine against using force.
In Washington, the U.S. said any move by Russia into eastern Ukraine would be a "very serious escalation" that could bring further sanctions.
An activist wearing a helmet stands behind a barricadeat the regional government building in Donetsk, Ukraine, Monday.
White House spokesman Jay Carney said there was strong evidence that some of the pro-Russian protesters were hired and were not local residents.
At the same time, the U.S. announced that Secretary of State John Kerry will meet with top diplomats from Russia, Ukraine and the European Union in a new push to ease tensions. The meeting, the first such four-way talks since the crisis erupted, will take place in the next 10 days, the State Department said.
Pro-Russian activists who seized the provincial administrative building in the city of Donetsk over the weekend announced the formation Monday of the independent Donetsk People's Republic.
They also called for a referendum on the secession of the Donetsk region, to be held no later than May 11, according to the Russian news agency Interfax.
A similar action was taken in another Russian-speaking city in the east, Kharkiv, where pro-Moscow activists proclaimed a "sovereign Kharkiv People's Republic."
It quoted the regional police as saying they later cleared the regional administration building, and the activists responded by throwing firebombs and rocks at the windows and setting tires ablaze. Local news reports said that the pro-Russian crowds then recaptured the building.
Kharkiv Mayor Gennady Kernes said the activists also took control of the TV tower in Kharkiv and demanded it resume broadcasting banned Russian channels.