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 . The were no casualties in the incident , separatist spokesman Vasiliy Nikitin said . The fight involved about 150 fighters on each side , he said . Bolotov had gone to Russia for medical treatment after being wounded on Tuesday . Tensions remain high across the country 's east , with just over a week to go before May 25 presidential elections . Separatist groups have declared `` people 's republics '' in both Luhansk and Donetsk . Neither the West nor the interim government in Kiev consider the two regions ' referendum on independence as legitimate . State Department spokeswoman Jen Psaki said the U.S. government rejects Denis Pushilin , the self-declared leader of the Donetsk People 's Republic , who asserted earlier this week that his region is not only independent , but also will ask to join Russia . `` These pro-Russia separatists have never been elected and do not represent the people of the region , '' Psaki said Saturday . `` ... Any decisions made about Ukraine must be taken by those with lawful authority , representing the citizens of Ukraine as a whole , and not under threat of foreign military intervention . '' Separatist leader : Donetsk region asking to join Russia . Russia slams Kiev military operation . Russia 's Foreign Ministry called Saturday for an end to what the Kiev government describes as an anti-terrorist operation against the separatists -- and questioned whether it was possible to hold elections given the militarized situation . In its statement , the ministry accused Ukrainian troops backed by aircraft of trying to storm the town of Slovyansk and of using heavy artillery to shell `` civilian installations . '' `` Such punitive action against its own citizens shows the hypocrisy of the Kiev authorities , '' the statement said , referring to an international pact agreed to last month which called for an end to violence . Ukraine 's official news agency Ukrinform cited the nation 's Defense Ministry Saturday as saying that Ukrainian forces continue to `` fully control '' the situation around Slovyansk , a stronghold of pro-Russia militants . The militants have put up 27 barricades around the town , where they still hold a number of public buildings , the Defense Ministry is quoted as saying . Report : Human rights worsening . A U.N. report released Friday shows an `` alarming deterioration '' of human rights in eastern Ukraine , said the U.N. high commissioner for human rights , Navi Pillay . The report paints a troubling picture , citing cases of targeted killings , torture , beatings , abductions and sexual harassment , as well as intimidation of the media . It also highlighted serious problems in Crimea , Ukraine 's Black Sea peninsula that was annexed by Russia in March , particularly for the minority ethnic Tatar population . Russia 's Foreign Ministry dismissed the findings of the U.N. report , saying it showed a `` complete lack of objectivity , total inconsistencies and double standards . '' Kiev and the West have condemned the annexation of Crimea and accuse Moscow of backing the pro-Russia militants in Ukraine 's east . Moscow blames the unrest in Ukraine on far-right ultranationalist groups . Journalist Victoria Butenko reported from Kiev and Laura Smith-Spark wrote in London . CNN 's Radina Gigova and Arkady Irshenko contributed to this report .
NEW : Ukraine spokeswoman : Irshenko leader in Ukraine does n't represent region . Ukraine 's border service says armed men freed a detained separatist leader . Luhansk 's `` people 's governor '' Luhansk was wanted by the security service . Tensions remain high in eastern Ukraine , with presidential elections Friday away .