Kiev, Ukraine (CNN) -- Armed men clashed with Ukrainian border guards Saturday after a separatist leader was detained at a checkpoint. He was trying to re-enter the country from Russia, the Ukrainian Border Service said. The incident is the latest violent flare-up in eastern Ukraine, where pro-Russia separatists staged a referendum on independence last weekend. Luhansk's self-declared "people's governor" Valeriy Bolotov -- who is wanted by Ukraine's Security Service -- was stopped at the Dovzhanskiy checkpoint, the border service statement said. Following his detention, about 200 armed men arrived at the checkpoint and demanded his release. The border guards tried to avoid bloodshed, but after an altercation, shots were fired. In the ensuing armed assault on the checkpoint, "the attackers" were able to take back Bolotov, the statement said.
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NEW: U.S. spokeswoman: Separatist leader in Donetsk doesn't represent region
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Ukraine's border service says armed men freed a detained separatist leader
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Luhansk's "people's governor" Valeriy Bolotov was wanted by the security service
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Tensions remain high in eastern Ukraine, with presidential elections just over a week away
Separatist groups have declared "people's republics" in both Luhansk and @placeholder.