The Donetsk People's Republic has giving the Kiev government until 9 p.m. local time on Thursday to remove Ukrainian troops from the Donbass region, a spokesman said, threatening to oust them by force if the ultimatum expires.
The leaders of the Donetsk militia on Wednesday night gave authorities 24 hours, until 6 p.m. GMT, to vacate roadblocks in the region, news agency Interfax reported Thursday.
"Reconnaissance groups and sabotage groups are ready to go and some are already in position," militia deputy commander Sergei Zrilyuk said Thursday, RIA Novosti reported.
The group has enough resources to ensure "everything will be destroyed and burned," if the conditions are not met on time, Zrilyuk was quoted as saying.
The ultimatum, issued just days after separatists in Donetsk claimed 90 percent support in a referendum on self-rule, does nothing to stem concerns that civil war could yet break out in Ukraine.
In the aftermath of Sunday's referendum, the Donetsk region has declared itself a people's republic, saying it no longer recognized the legal authority of the interim authorities in Kiev.