Rebels in the the town of Slovyansk, who control the local police station and security service office, issued a bold call for help from Russian President Vladimir Putin on Monday, when it had been expected the town would be the focus of a Ukrainian government operation involving the army.

"We call on Russia to protect us and not allow the genocide of the people of Donbas (Donetsk region)," said rebel leader Vyacheslav Ponomaryov.

The comments came after the expiration of a deadline early on Monday morning, which Kyiv had imposed on pro-Russia gunmen in eastern Ukraine to drop their weapons and vacate buildings they had seized in at least nine cities. Rather than heeding the ultimatum, violence continued throughout the day.

A pro-Russian group stormed a police station in the city of Horlivka, which lies near the Russian border, and raised the Russian flag on the roof of the building. Later, armed men in masks seized a military airport outside Slovyansk.

While there was no sign of action by Ukrainian security forces to force the gunmen out from their barricades, acting Ukrainian President Oleksandr Turchynov has reportedly raised the possibility of a joint operation with United Nations peacekeepers. However, such an operation appears unlikely, as Russia holds a veto on the UN Security Council, which has to authorize any peacekeeping operation.

"The Russian Federation is sending special units to the east of our country, which seize administrative buildings with the use of weapons and are putting the lives of hundreds of thousands of our citizens in danger," said a statement from Turchynov on the presidential website.

Russian news agencies quoted a Putin spokesman, Dmitry Peskov, as saying the president had received "numerous appeals" for help from eastern Ukraine. Peskov said Putin was watching developments with "great concern."

Turchynov suggests referendum

The separatists' uprising began eight days ago but has accelerated in the past 48 hours. They are demanding more autonomy from the new government in Kyiv and closer ties with Russia.

On Monday, Turchynov indicated Ukraine could hold a nationwide referendum on the future shape of the country, and suggested that it could be held at the same time as a presidental election on May 25. The pro-Russian side wants referendums to be held, but only in the east of the country, which Kyiv asserts is illegal.

The government in Kyiv, along with Western officials, have accused Moscow of instigating the unrest in eastern Ukraine, saying the events are similar to the situation that unfolded in Crimea, which ended with its annexation by Russia.

jr/pfd (AFP, AP)