Pro-Russia militants seized another government building in eastern Ukraine Monday, hours after a deadline set by the Ukrainian government for gunmen to surrender their weapons passed early Monday, with no immediate sign of any action to force the insurgents out.

The Associated Press reported that dozens of angry men hurled rocks, smashed windows and broke into a police station in the city of Horlivka not far from the border with Russia, while hundreds of onlookers cheered them on. Thick white smoke rose from the entrance to the building.

Later in the day, armed men in masks also seized control of a military airport outside the city Slovyansk, also in the Donetsk region.

The events in Horlivka were the latest sign of trouble in Russian-speaking eastern and southern regions, in which pro-Russian gunmen have seized a number of government buildings demanding more autonomy from the central government and closer ties with Russia.

Ukraine's acting President Oleksandr Turchynov called for the deployment of United Nations peacekeeping troops in the country’s eastern region Monday, where pro-Russian insurgents have occupied buildings in nearly 10 cities.

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In a phone conversation with Secretary-General Ban Ki Moon, Turchynov suggested that an "anti-terrorist operation" could be conducted jointly by Ukrainian security forces and U.N. peacekeepers, according to the presidential web site.

Peacekeepers would have to be authorized by the U.N. Security Council, in which Russia holds a veto.

Kiev authorities and Western officials have accused Moscow of instigating the protests, saying the events echoed those in Crimea, which was annexed by Russia last month. Ever since pro-Russian President Viktor Yanukovych fled to Russia in late February, Russia has demanded constitutional reforms that would turn Ukraine into a loose federal state.

After staunchly refusing such demands, acting President Oleksandr Turchynov indicated Monday that holding a nation-wide referendum on the nation's status was a possibility and that such a vote could be conducted on May 25, along with presidential elections, the Interfax news agency reported.

Meanwhile, a deadline set by the Ukrainian government for pro-Russian gunmen to leave government buildings in eastern Ukraine and surrender weapons passed early Monday, but the insurgents remain with no sign of any future action to remove them.

Turchynov had issued a decree Sunday that those protesters who disarm and vacate government offices in several cities in the Russian-leaning east of the country by 9 a.m. local time Monday would not be prosecuted. Turchynov vowed that a "large-scale anti-terrorist operation" would take place to re-establish control over those areas and that the fate of the Crimean Peninsula, annexed by Russia last month, will not be repeated.

There was no immediate comment from the government on the deadline passing.

But Serhiy Taruta, governor of the Donetsk region, where government buildings in several cities, including the regional capital Donetsk, have been seized by pro-Russian gunmen, said an anti-terrorist operation was underway in the region, according to the Interfax news agency.

Taruta did not give any details of what the anti-terrorist operation would entail. The governor usually does not have authority to launch anti-terrorist measures on his own and he was likely acting on the orders of top security officials in Kiev.

Taruta said the anti-terrorism measures were aimed at "protecting the peace and order on our land, which today is being taken away from us by armed, aggressive fanatics cynically and cold-bloodedly," he was quoted as saying. "They are terrorists and we will not let them rule on our land."

The West has accused Moscow of fomenting the unrest. Ukraine's ousted president, Viktor Yanukovych, claimed that the Kiev government was coordinating its actions with the CIA.

European Union foreign ministers met in Luxembourg to consider further sanctions against Russia Monday. Russia has warned the Kiev government against using force against the protesters in the east and has threatened to cancel an international diplomatic conference on the Ukrainian conflict scheduled for later this week.

The Associated Press contributed to this report.