Oleksandr Turchynov said the body of politician Vladimir Rybak was found near rebel-held Sloviansk.
“The terrorists who effectively took the whole Donetsk region hostage have now gone too far,” he said. . . .
In another incident, a Ukrainian military surveillance plane was hit by small arms fire over eastern Ukraine, the defence ministry said.
The aircraft, an Antonov AN-30, suffered minor damage over Sloviansk when it was targeted by automatic gunfire, according to the ministry. No-one was hurt and the plane returned safely to Kiev.
The funerals have meanwhile taken place of three men shot on Sunday during a raid on a checkpoint manned by pro-Russian separatists near Sloviansk.
The local separatists said the attack was carried out by ultra-nationalist Right Sector militants but Kiev called it a “provocation” staged by Russian special forces.
The bodies of those killed lay in open coffins at the funeral ceremony at the Church of the Holy Spirit in the centre of Sloviansk.
When the coffins were carried out of the church, the crowd outside shouted “Glory to the Heroes of the Donbass!” over and over again – Donbass being the name for the Don River basin. Church bells rang out.
The people I’ve been speaking to here are convinced that it was Ukrainian ultra-nationalists who carried out Sunday’s attack. One woman told me she was proud to be Ukrainian, but that instability and violence was pushing people here to want closer ties to Russia.