Ukraine's interior minister has warned pro-Russian activists who have taken over state buildings in eastern cities to enter talks to find a political solution or face "force".Arsen Avakov said the situation would "be resolved in 48 hours" either way.Earlier, a number of people held inside a state security building in Luhansk since Sunday were freed.The EU, Russia, US and Ukraine are to meet next week in the first four-way meeting since the crisis erupted.The talks are aimed at breaking the impasse since Russia annexed the southern Ukrainian peninsula of Crimea in February. Russian troops are now massed along the borders of the two countries.'Forceful answer'Mr Avakov said an "anti-terrorist operation" was under way in the regions of Luhansk, Donetsk and Kharkiv and would be concluded within the next two days."There are two options," he told journalists, "political and negotiations - and force."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."Shortly before he spoke, Ukraine's security service said 56 people held inside its Luhansk offices had been allowed to leave following two rounds of negotiations with local politicians.On Tuesday, it said "radicals" were armed and holding 60 people against their will. It is not clear exactly how many people remain in the building.During a rally outside the building overnight, speakers condemned the interim leadership in Kiev and repeated their call for a referendum on whether to seek greater regional autonomy, the Associated Press reports.Ukraine's authorities said on Tuesday they had retaken control of the government building in Kharkiv, but protesters remain in control of the regional authority building in Donetsk.Barricades of barbed wire, tyres and even car bumpers surround the buildings.Moscow has warned Ukraine that using force to end the protests could lead to civil war.On Wednesday, German Chancellor Angela Merkel criticised Russia for not doing enough to ease the tension.She told parliament: "Unfortunately, in many areas it is not clear that Russia is contributing to a de-escalation of the situation."'Genuine dialogue'US Secretary of State John Kerry said Russian special forces and agents had been "the catalyst behind the chaos of the last 24 hours".He said the events "could potentially be a contrived pretext for military intervention just as we saw in Crimea".Russia's President Vladimir Putin says there is no intention to invade Ukraine but he reserves the right to protect Russian interests there.But he said Russia would "engage in a genuine dialogue with the Ukrainian authorities".Foreign Minister Sergei Lavrov will meet Mr Kerry, EU foreign policy chief Catherine Ashton and Ukraine's Foreign Minister Andriy Deshchytsia next week.Kiev and its allies accuse Moscow of fomenting unrest in the mainly Russian-speaking east of the country as a pretext to possibly seizing more territory - a claim strongly refuted by Russia.On Wednesday, Moscow again denied any intent behind its forces along the Ukraine border."The United States and Ukraine have no reason to be worried," the foreign ministry said in a statement."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."Moscow has so far refused to recognise the new authorities in Kiev following the ousting of pro-Russian President Viktor Yanukovych in February.(BBC)ANN.Az