* Rifles visible inside building
* Protesters want referendum on status of region
* State security building occupied since Sunday
By Thomas Grove
LUHANSK, Ukraine, April 8 (Reuters) - Past the barricades of metal railings, sandbags and barbed wire, Russian separatists peer out of the state security building in the eastern Ukrainian city of Luhansk, rifles in hand.
The headquarters of the former KGB in this small Ukrainian city less than 30 km (20 miles) from the Russian border is potentially the most dangerous flashpoint among buildings in eastern Ukraine seized on Sunday night by pro-Moscow agitators.
Activists inside have seized an armoury of automatic rifles. The Ukrainian security service says they have also wired the building with explosives and are holding around 60 people there against their will, although the activists deny this.
They say they are here for as long as it takes to force a referendum on the region's status within Ukraine.
"I'll stay here until the end, until victory. Once you've taken up arms, there's no turning back," said Andrei, one of the men inside, who refused to give his family name.
Holding a police shield, he confirmed that protesters had found the arsenal of weapons stored in the security building - around 200-300 Kalashnikovs, he said, and some stun grenades.
"There are no explosives, no hostages. We do not need hostages to get what we want," said Anton, a protester who described himself as one of the coordinators of the action.
Ukrainian authorities say the pro-Moscow agitation in cities in the east of the country is an attempt to replay the events in Crimea, a region Russian forces seized and annexed last month. Washington blames Russian spies and special forces for stirring up the unrest and says it could be the precursor to an invasion.
Police cleared pro-Russian protesters from a building in the city of Kharkiv overnight, but the activists are still occupying the regional government headquarters in Donetsk as well as the Luhansk security building.
In Luhansk, there is so far no sign of the authorities moving against the former KGB building, where scores of armed protesters are believed to be inside. Police kept well away, with only a few officers standing at a nearby intersection.
Hundreds of pro-Moscow activists waving Russian flags were gathered outside the building, where windows have been broken, and the facade smashed. The protesters have hung a Soviet hammer and sickle and red star slightly askew above the entranceway. At least three rifles were visible through the broken windows.
After two days of occupation, protesters were bringing in dry pasta, instant coffee and cigarettes. With electricity no longer on in the building, demonstrators found a generator to keep a loud hailer working outside the building.
"If one shot is fired, Putin will send the troops in!" said one woman over the speakers to hundreds of people gathered outside the building, who chanted in response: "Russia! Russia!"
"But may guardian angels protect you! Don't be afraid!" she yelled back.
Protesters have already called for a referendum, similar to the one that paved the way for Crimea's accession to Russia in March, sparking accusations from Prime Minister Arseny Yatseniuk that President Vladimir Putin was trying to split up Ukraine.
Police were not available for comment. At the regional police headquarters, piles of sandbags lay just inside the entrance: "In case they try to take over our buildings," said a police officer at the front desk who declined to give his name.
In downtown Luhansk, a city of almost half a million people known for metallurgy and heavy industry like much of eastern Ukraine, there is no love for Kiev's government, widely believed here to ignore the rights of Russian speakers.
Many said they resented the government for switching off Russian state television, and for an abortive vote by Kiev lawmakers to downgrade the status of the Russian language.
"I don't want to be part of the European Union. It might be nice to visit, but Russia is where my family is, my relatives, my friends," said Larisa Klass, 64, a librarian at Luhansk's Gorky Library. "That's why we have to find a solution either federalism or separatism." (Reporting by Thomas Grove; Editing by Richard Balmforth and Peter Graff)