US President Barack Obama and German Chancellor Angela Merkel will discuss the escalating Ukraine crisis on today in their White House meeting.
Kiev meanwhile decided to to reinstate conscription as insurgents tightened their grip over more than a dozen eastern cities and towns.
Around 300 militants hurling petrol bombs and bricks stormed the six-storey prosecutor´s building in Donetsk, beating up outnumbered riot police and stripping them of their shields and batons.
Ukrainian media reported that a prosecutor´s office in the town of Horlivka and a police station in Krasnoarmiysk were also overrun.
The violence took place even as mass pro-Russia rallies were held in Donetsk and in annexed Crimea.
Kiev´s Western-backed government has admitted its security forces are helpless to halt the expanding rebellion.