Protesters in Donetsk and gunmen in Slovanysk and Krasny Liman seized police stations, adding to the government buildings they are occupying.
According to witnesses, the unmarked gunmen in Slovanysk and Krasny Liman spoke Russian and quickly raised Russian flags over the buildings.
It is believed that they may be the same Russian special forces who covertly led the invasion of Crimea, pretending to be militias.
Tensions had been lessening, over the past few days while negotiations seemed to be moving forward.
However, Saturday's hostile actions have put an end to negotiations and brought the promise of a swift and harsh response from the Ukrainian government.
Interior Minister Arsen Avakov promised that there would be "zero tolerance for armed terrorists".
He also stated that shots were fired in Kramatorsk, where police defended their station from gunmen.
The Ukrainian government and western governments have blamed Russia for causing much of the current troubles.
Russia has maintained a presence of as many as fifty thousand troops, along the border, which has caused fears they may invade.
The international community condemned and declared Russia's takeover of Crime to be illegal, however no way of making them leave has been found.
