Pro-Russian separatists have seized the regional government headquarters in Luhansk, one of the largest cities in eastern Ukraine.

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Pro-Russian activists attack the regional administration building in Luhansk, eastern UkraineReuters

About 1,000 demonstrators gathered in front of the building and watched as activists, some masked and wielding baseball bats, broke into the building without resistance.

Later protesters allowed police who had been inside the building to leave peacefully. Luhansk, a city of about 450,000, is just 25km west of the border with Russia.

The action further increases tensions in the east, where insurgents have seized control of police stations and other government buildings in at least 10 cities and towns.

Activists waving a Russian flag break into the regional administration building in LuhanskReuters
Pro-Russian activists explore the newly seized regional government headquarters in LuhanskReuters
Ukrainian interior ministry members leave the regional administration headquarters. Hundreds of pro-Russian separatists stormed the headquarters, unopposed by policeReuters
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Ukrainian government security forces ushered out of Luhansk HQ by masked insurgentsReuters
A pro-Russian activist holds a beautifully decorated mace outside the regional government headquarters in LuhanskReuters

On Monday evening, a pro-Ukrainian rally in Donetsk was attacked by several hundred armed men shouting "Russia!"

Police attempted to hold them back but then stood aside as dozens of protesters were battered.

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Pro-Russian and pro-Ukrainian supporters clash in Donetsk, eastern Ukraine. Several people were wounded when pro-Russian separatists attacked a rally in support of Ukrainian unityReuters
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A pro-Russian protester walks in front of riot police during a pro-Ukraine rally in the eastern city of Donetsk. Several people were wounded when what appeared to be stun grenades exploded during a rally in support of Ukrainian unityReuters
Police regroup after a clash between pro-Russian and pro-government activists in DonetskGetty
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An injured man receives treatment from an ambulance crew after a pro-Ukrainian rally in Donetsk erupted in clashesReuters
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A wounded pro-Russian activist joins other activists after clashing with pro-Ukrainian supporters during a rally and march in DonetskGetty

Armed insurgents, which the West says are tacitly backed by Moscow, are seeking more autonomy in eastern Ukraine — and possibly even independence or annexation with Russia. Ukraine's acting government and the West have accused Russia of orchestrating the unrest, which they fear Moscow could use as a pretext for an invasion.

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Masked separatists raise their flag on a government building in Donetsk...Reuters
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...and throw away the Ukrainian flagReuters
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An armed man in military fatigues and orange and black pro-Russia St George ribbons holds a machine gun with a "People's Republic of Donetsk" sticker on it outside the SBU regional building in SlavianskAFP
A pro-Russian armed man poses with a child in front of the seized town administration building in KostyantynivkaReuters