Ukrainian security services say pro-Russian separatists have placed explosives in a seized building in Luhansk and are holding around 60 people against their will.
"The anti-terror group of the security services of Ukraine (SBU) .. has established that the criminals have mined the building...and are holding around 60 people, threatening them with weapons and explosives," the SBU said in a statement.
Tensions remain high in eastern Ukraine after at least three died in a day of shooting during what was supposed to be an Easter truce.
In an exclusive interview with NBC News, the Ukrainian Prime Minister warns of the dangers of unchecked Russian expansion and aggression.
Russia, the US and the EU say that all sides have agreed to steps to "de-escalate" the crisis in Ukraine at talks in Geneva.