Ukraine's Security Service confirmed 56 people held inside an official building in the eastern city of Luhansk, which is occupied by pro-Russian separatists, have been allowed to leave the premises.
The Luhansk security services building was among several government offices seized by pro-Moscow groups on Sunday in an escalation of protests against the interim government in power since the ouster of President Viktor Yanukovych in February.
All the cities affected by the uprisings are in Ukraine's industrial heartland in the east, which has a large population of ethnic Russians and where hostility is strong towards the new administration.
As of Wednesday morning, protesters in Luhansk had erected high barricades along a thoroughfare running in front of the security service premises.
Security services said on Tuesday that separatists inside the building, armed with explosives and other weapons, were holding 60 people hostage. It was not immediately clear if the 56 allowed to leave on Wednesday were among that number, or how many people were still being held.
Overnight, speakers at a gathering in front of the building condemned the government in Kiev and renewed demands to be allowed to hold a referendum on declaring autonomy for their region. That demand is similar to one that preceded Crimea's annexation by Russia.
Speeches were occasionally interspersed with chants of "Russia, Russia!"
An unidentified speaker at one stage listed names of prominent politicians that he suggested should be executed, eliciting cheers in return.
Those occupying the building have issued a video statement warning that any attempt to storm the place would be met with armed force.
In the video, posted by Ukrainian media, a masked man identified the occupiers as Ukrainian veterans of the Soviet war in Afghanistan and said that if authorities try to retake the building, "Welcome to hell, then!"
There was little immediate evidence of any major deployment of Ukrainian special forces at the site.
The security service said negotiations with the separatists were continuing and that parliament deputies had been able to enter and leave the building unhindered.
The Ukrainian government and the US have accused Moscow of fomenting the unrest as a pretext for another Russian military incursion like the takeover of Crimea last month. Up to 40,000 Russian troops are massed along the Ukrainian border, according to Nato.