A small group of gunmen on Saturday seized a police station in Ukraine's restive eastern industrial heartland amid escalating protests in favour of the heavily Russified region joining Kremlin rule.
Ukraine's Interior Minister Arsen Avakov said another group of gunmen also tried to take control of the Donetsk region's prosecutor's office but was repelled.
The early dawn raid on the police station happened in the town of Slavyansk -- about 60 kilometres (35 miles) north of the regional capital Donetsk.
The Donetsk adminstration centre is already under the control of several hundred gunmen who have proclaimed the creation of their own "people's republic" and called on President Vladimir Putin to send Russian troops into eastern Ukraine.
"Armed men in camouflage fatigues have taken the police station in Slavyansk," Avakov wrote on his Facebook page. "Here, our response will be very severe."
A local police official told Kiev's private Channel Five television that the raid was staged by six men who had fired several shots into the air before storming the station.
It was not immediately clear how the local police responded to the attack or whether the gunmen had taken any hostages.
But Avakov said that Ukrainian special forces had been dispatched to the scene.
"There is zero tolerance for armed terrorists," he said.
The interior minister added that a separate group of assailants had tried to take control of the prosecutor's office building the regional capital Donetsk.
"They have all been expelled. The building has been clear of unauthorised personnel," he wrote.
"Another self-declared defence minister has been arrested," he added.
An AFP reporter saw a heavy police presence around the prosecutor's office and the building under apparent government control.
State buildings still held
Avakov has emerged as one of the more hawkish ministers in the interim pro-Western leadership that toppled a Kremlin backed regime in Kiev in February and sought to link the ex-Soviet state's future with the West.
The interior minister had on Wednesday issued a veiled 48-hour ultimatum for the separatists holding the Donetsk government seat to lay down their arms or face the possible of use of force.
But no action followed and the Donetsk administration building along with a security office in the nearby city of Lugansk remained under the separatists' control for the sixth day running on Saturday.
Ukraine's embattled Prime Minister Arseniy Avakov had promised during an unannounced visit to Donetsk on Friday to grant more powers to the country's regions and never to clamp down on the east's right to use the Russian language.
"No one under any circumstances will restrict the use of a language that a person is accustomed to using," Yatsenyuk told local officials.
He also admitted that he "must respond to people's desire to have more regional authority."
"We will implement this task within the framework of constitutional reforms," said Yatsenyuk.
Kiev has previously said it was ready to grant more powers to the regions while stopping well short of creating the federation sought by Russia.
Yatsenyuk's attempt to end the occupations failed in part because both the Donetsk and Lugansk gunmen also want to stage an independence referendums coinciding with snap presidential polls Ukraine will stage on May 25.
Ukraine's new authorities reject that condition outright because a similar referendum last month in Crimea led to the Black Sea peninsula's seizure by Russia.
Russia's foreign ministry warned on Friday that Moscow would boycott the first round of international peace talks with Kiev that have been arranged by US and EU officials for Thursday should Ukraine use force against the militants.