Pro-Russian activists in Sloviansk, eastern Ukraine, have begun negotiations with the Kyiv authorities on the possible release of Organization for Security and Cooperation in Europe (OSCE) observers in exchange for detained protesters, Sloviansk "people's mayor" Viacheslav Ponomariov told Interfax.

"These OSCE representatives remain in Sloviansk. We have created comfortable conditions for them. We are treating them as friends. Of course, they want to go home, and we are already holding such negotiations with the Kyiv authorities. We hope that we will be able to exchange them for our activists held by Kyiv," he said.

Three soldiers of the Ukrainian Security Service's Alfa special operations unit detained by the local self-defense forces remain in Sloviansk as well, he said.

"They are feeling normal. We will also try to exchange them," Ponomaryov said.

The situation is Sloviansk is quiet, he added.

"We had been bracing for an overnight storm of the city, but it did not take place for some reason. Everything is quiet now. People are preparing to attend May 1 demonstrations,' he said.

Unidentified men stopped a bus carrying OSCE inspectors on the outskirts of Sloviansk on April 25 and escorted the bus to the city.

The eight-member OSCE group is comprised of four experts from Germany and one each from Sweden, Poland, Denmark and the Czech Republic. Swedish OSCE expert Ingvi Thomas Johanson, who suffers from diabetes, was later released.