* Police say no hostages being held in Luhansk
* 50 protesters leave building, others to fight on
* Talks with authorities continuing (Adds news conference with separatists inside building)
By Thomas Grove
LUHANSK, Ukraine, April 9 (Reuters) - Pro-Russian separatists reinforced barricades around the state security building in the eastern Ukrainian city of Luhansk on Wednesday and called on President Vladimir Putin for help after the government warned it could use force to restore order.
Protesters were also engaged in talks to ease the standoff, which Kiev has said could provide a pretext for a Russian invasion, and lawmakers from eastern Ukraine proposed an amnesty for protesters to defuse tension.
The former KGB headquarters is one of three government buildings seized this week in eastern Ukraine by protesters demanding regional referendums on independence from Kiev.
Tensions have risen in the mainly Russian-speaking east since the overthrow of Ukraine's Moscow-backed president and the installation of a new pro-European government.
"Of course we must ask Russia to take us in because I don't see an alternative," said a man dressed in camouflage who gave his name as Vasiliy and said he was the commandant of the building. "Putin help us!" he said.
In a news conference held inside the occupied building late on Wednesday, Valery Bolikov, who said he was a representative of headquarters of the Southern and Eastern Army, said talks with authorities had failed to yet bring an agreement.
"Talks are continuing there are a few issues which are being dealt with but they haven't come to their logical conclusion," he said in Ukraine's Security Services ornate conference hall.
While some protesters have championed the idea of joining Russia like Crimea, Bolikov said that their demands went no further than a referendum to vote whether to give Luhansk more autonomy as part of a federal structure in Ukraine.
"(We will leave the building) only after the fulfillment of our demands of the carrying out of a referendum on federalisation," he said.
Outside of the conference hall, masked men armed with kalashnikovs, pistols and guns lined the building's many corridors. Tensions around the seizure of the building rose after the protesters broke into the security service's arsenal.
One protesters put the arsenal at around 200-300 rifles.
Local police spokeswoman Tatyana Pogukai said that police were not taking any action while negotiations were ongoing.
"We don't want any violence. No one needs any death or blood," she said over the telephone.
Protesters in Donetsk, to the south, remain in control of the main regional authority building, but authorities have ended the occupation in the city of Kharkiv.
"A resolution to this crisis will be found within the next 48 hours," Interior Minister Arsen Avakov told reporters in the capital Kiev.
"For those who want dialogue, we propose talks and a political solution. For the minority who want conflict they will get a forceful answer from the Ukrainian authorities," he said.
Ukraine's state security service said that 50 people had left the building in Luhansk overnight. Protesters confirmed that some had left.
"Those who left were not ready to stay and fight," said Vasiliy, who said his "soldiers" would fight on until a referendum on independence from Kiev was held.
Occupation leaders said those who stayed behind were trained soldiers who had fought in Chechnya and Afghanistan.
"We won't be the first ones to fire a shot but we will defend ourselves," said Pavel Strupchevsky.
Protesters insist that they have no help from Russia and that no Russians are among their ranks, but Ukraine's government says the actions are part of a Russian-led plan to dismember the country, a charge Moscow denies.
U.S. Secretary of State John Kerry accused Russian agents and special forces on Tuesday of stirring up separatist unrest and said Moscow could be trying to prepare for military action as it had in Crimea.
Russia denied the accusations on Wednesday and dismissed concerns over a troop buildup near the border with Ukraine in what has become the worst East-West crisis since the end of the Cold War in 1991.
"Russia has stated many times that it is not carrying out any unusual or unplanned activity on its territory near the border with Ukraine that would be of military significance," the Russian Foreign Ministry said.
A lawmaker from the most popular political party in the east, the Party of Regions, on Wednesday said he planned to ask parliament to amnesty the protesters, following the success of a similar move to reduce tension in Kiev two months ago.
"The situation is so tense and complex that one stray word might cause a flare-up," said Oleksandr Yefremov. "To prevent people suffering ... we are proposing a draft law on an amnesty." (Additional reporting by Pavel Polityuk and Richard Balmforth; Writing by Conor Humphries and Tom Grove; Editing by Giles Elgood and Andrew Hay)