SLAVYANSK, Ukraine - Pro-Russian Ukrainian rebels holding captive an international team of military observers from the OSCE said Sunday they are “prisoners of war” and brought them before the media in a news conference.

The group of eight men, all Europeans, were part of a 12-member OSCE military verification team being held in east Ukraine. The other four are Ukrainian military officers who were not brought before the press. Speaking through one of their number, a German officer, the Europeans asserted their diplomatic status to the scores of local and foreign journalists assembled in the town of Slavyansk. With armed rebels watching over them as they spoke, the group said they were in good health.

They said they had been “captured” by the insurgents on Friday, around four kilometres (two miles) outside Slavyansk as they had been about to return to the regional hub city of Donetsk.

“We are OSCE officers with diplomatic status,” German officer Axel Schneider said. “I cannot go home of my free will.”

Schneider added that he did not know the whereabouts of the four Ukrainian officers grabbed with them. The Organisation for Security and Cooperation in Europe said it has sent a negotiating team to Slavyansk to try to arrange the entire team’s release.

Earlier, the local rebel leader in the town, Vyacheslav Ponomaryov, told AFP and a small group of other reporters the OSCE observers were considered “prisoners of war”. “In our town, where a war situation is going on, any military personnel who don’t have our permission are considered prisoners of war.”

Ponomaryov, who was wearing a pistol in a holster and was escorted by two armed bodyguards, claimed in the same interview that the observers “are not our hostages — they are our guests”.

The rebel leader said all “are doing well”. He added that the group’s driver, who had been seized with them on Friday, had been released. He repeated in the interview that the men would only be freed in exchange for Kiev’s authorities releasing arrested pro-Moscow militants.

And he stressed that the rebels did not consider the detained men part of the main OSCE monitoring mission deployed in Ukraine.

The OSCE headquarters in Vienna has said the military verification mission is indeed a separate operation, under German command.

The pan-European security body said two monitors from its main mission were also held briefly Sunday at a checkpoint in eastern Ukraine, before Ukrainian police secured their release.

Late Sunday, Ukraine’s foreign ministry said OSCE Secretary General Lamberto Zannier was heading to Kiev over the hostage drama.

Asked about Russia’s promise to try to convince the pro-Kremlin rebels to release the observers, Ponomaryov said: “I have no direct contact with Moscow.”

Ponomaryov also said that rebels had separately “arrested” three Ukrainian officers — a colonel, a major and a captain — he said had been sent towards Slavyansk on a spying mission.

“There were a total of seven in their group and we arrested three of them. We will swiftly get the four others,” he said.

The three officers were being kept in Slavyansk. Ukraine’s SBU security service confirmed they had been seized.

The rebel mayor said there would be no negotiation with Kiev over the imprisoned Ukrainians because the pro-Kremlin insurgents see the capital’s Western-backed government as illegitimate.

“There will be no contact with Kiev, only through the intermediary of the OSCE,” he said. Ukraine’s authorities, he said, “understand only the language of force”.

Slavyansk has become the epicentre of the military standoff in eastern Ukraine where pro-Russian militants are defying Western pressure to exit occupied buildings.

The Ukrainian army has set up a siege operation around the town of 110,000 people to prevent reinforcements reaching the rebels but has stressed it will take a measured response in its military operations in a bid to avoid civilian casualties.