SLOVYANSK, Ukraine - Pro-Russian militants in camouflage fatigues and black balaclavas paraded captive European military observers before the media on Sunday, hours after three captured Ukrainian security guards were shown bloodied, blindfolded, and stripped of their trousers and shoes, their arms bound with packing tape.

The provocative displays came as the increasingly ruthless pro-Russian insurgency in the east turns to kidnapping as an ominous new tactic.

Dozens of people are being held hostage, including journalists and pro-Ukraine activists, in makeshift jails in Slovyansk, the heart of the separatists' territory, as the pro-Russian insurgents strengthen their control in defiance of the interim government in Kiev and its Western supporters.

In deliberate and clipped phrases, Col. Axel Schneider of Germany, speaking on behalf of the observers, insisted they were not NATO spies, as claimed by the insurgents, but a military observation mission operating under the auspices of the Organization of Security and Cooperation in Europe.

"We are not fighters, we are diplomats in uniform," he said, noting that his unarmed team included an officer from Sweden, which is not a NATO member.

The observers appeared nervous as they were escorted by the armed men into the Slovyansk city hall for the news conference.

Referring to himself and his team as "guests" under the "protection" of the city's self-proclaimed mayor, Schneider said they were being treated as well as possible under the circumstances.

He said his group, detained by pro-Russian militiamen outside Slovyansk on Friday, was kept in a basement before being moved.

The spectacle of accredited diplomats being presented to the media as what Slovyansk's insurgency-appointed mayor, Vyacheslav Ponomarev, has described as "bargaining chips" provoked disgust in European capitals. German Foreign Minister Frank-Walter Steinmeier condemned it as "revolting" and a violation of the men's dignity. Four members of the team are German.

One of the observers, Swedish Maj. Thomas Johansson, was released later in the day "on humanitarian grounds as he has a mild form of diabetes," said Stella Khorosheva, a spokeswoman for the Slovyansk mayor.

Also on Sunday, several hundred pro-Russia activists stormed the television broadcasting center in Donetsk, the regional capital of eastern Ukraine, to demand that Russian state channels be put back on the air. The Kiev government last month blocked broadcast of the Russian channels, which serve as propaganda tools for the Kremlin.

The U.S. and other nations in the Group of Seven have announced plans to impose additional economic sanctions on Russia in response to its actions in Ukraine. The European Union also is planning more sanctions, with ambassadors from the bloc's 28 members to meet Monday in Brussels to add to the list of Russian officials who have been hit by asset freezes and travel bans.