Clashes have escalated in eastern Ukraine after dozens of rebel fighters surrounded and stormed the separatist headquarters in Donetsk, in the most serious case of insurgent infighting seen so far. Pro-Russian forces from the Vostok Battalion broke through the regional government building and demanded activists from the so-called People's Republic of Donetsk - which was set up in April - leave the premises. The insurgents then arrested members of the rival group, before removing their flags from check-points in the area. Scroll down for videos Members of the Vostok Battalion, a pro-Russia militia, today surrounded separatist headquarters in the eastern Ukrainian city of Donetsk,  in what is believed to be the most serious case of insurgent infighting to date
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Insurgent fighters turned against each other as clashes in Ukraine escalated
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Pro-Russians stormed separatist HQ in Donetsk amid reports of looting
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They also removed flags from check-points and arrested rival groups
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It comes after helicopter was shot down with Russian anti-aircraft missiles
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Army General Serhiy Kulchytskiy among the dead in attack in Slovyansk
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Kulchytskiy once served in Soviet army and was head of combat training for Ukraine's National Guards
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Pro-Moscow rebels impose curfew in Donetsk after declaring martial law
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Reports suggest Kiev has sent armoured vehicles to the embattled city
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