Kalashnikov-wielding gunmen on Saturday seized a police station and a security building in Ukraine's restive eastern industrial heartland amid spreading protests to press for the heavily Russified region to join Kremlin rule.
The coordinated attacks and a subsequent raid by a few hundred pro-Russian protesters on the police headquarters of the local capital Donetsk underscored the volatility of the crisis ahead of first direct talks between EU and US diplomats and their Moscow and Kiev counterparts in Geneva on Thursday.
They also threaten to lead to further violence as far right forces who hold sway over the ex-Soviet state's western regions and who played a decisive role in this winter's anti-government protests watch the nation of 46 million veer toward a possible breakup.
Ukraine's foreign minister blamed the occupations on the "provocative activities of Russian special services" while a prominent nationalist called on militants in his Right Sector party -- branded as a neo-Nazi organisation by Moscow -- to "fully mobilise and prepare for decisive action".
Ukraine's interim government has been facing relentless pressure from Russia since its February ouster of an unpopular Kremlin-backed president and decision to seek closer ties with the West.
Moscow has massed tens of thousands of troops on Ukraine's eastern border after annexing the Black Sea peninsula of Crimea and nearly doubled the rates it charges Kiev for gas.
Russia is now ready to demand prepayment from the cash-strapped government for future gas deliveries or halt supplies -- a move that would impact at least 18 EU countries and deepen the worst East-West standoff since the Cold War.
But the seizures more immediately highlight how little sway Kiev's untested leaders have over pro-Russians who have since April 6 also controlled the Donetsk government seat and a state security building in the nearby eastern city of Lugansk.
- 'Armed terrorists' -
The morning police station raid and a subsequent attack of the regional security service centre happened in Slavyansk -- a riverside town of 100,000 about 60 kilometres (35 miles) north of the regional capital Donetsk.
Ukraine's interior ministry said the first assault was led by 20 "armed men in camouflage fatigues" whose main purpose was to seize 20 machine guns and 400 Makarov guns stored in the police headquarters "and to distribute them to protesters".
"Our response will be very severe," Interior Minister Arsen Avakov wrote on his Facebook page.
"There is zero tolerance for armed terrorists."
An AFP reporter saw the Slavyansk police station surrounded by armed men in masks and camouflage who had set up a barricade of old tyres and dumpsters in front of the police headquarters.
The gunmen aggressively shoved aside Western reporters and only allowed Russian-speaking media anywhere near the building.
"The entire city... will defend the guys who seized this building," Slavyansk Mayor Neli Shlepa told Russia's Life News television outside the police headquarters.
The interior ministry said some of the same gunmen had later occupied the city's state security service building.
"The protest participants are continuing to arm themselves with weapons seized from the police," the interior ministry said in a statement.
- 'People's republic' -
Ukraine's interior minister said that a separate group of assailants had also unsuccessfully tried to seize the Donetsk prosecutor's office.
But an AFP reporter in the city saw about 200 pro-Russian protesters armed with clubs and sticks storm the police headquarters and meet no resistance from anyone inside.
A few dozen anti-riot police who arrived at the scene were instead seen sporting orange and black ribbons symbolising support for Russian rule -- a vivid sign of Kiev's slipping hold on Ukraine's eastern rust belt.
The Donetsk administration centre is already being held by 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.
Ukraine's embattled Prime Minister Arseniy Yatsenyuk promised during an unannounced visit to Donetsk on Friday to grant more powers to the country's regions and protect the east's right to use the Russian language.
Kiev has previously said it was ready to back partial devolution while stopping well short of creating the federation sought by Russia.
But the Donetsk and Lugansk gunmen also want to stage independence referendums coinciding with snap presidential polls Ukraine will stage on May 25.
- 'Russian agents' -
Both Western leaders and Kiev have accused the Kremlin of orchestrating the unrest in order to justify a possible future invasion of eastern Ukraine -- a charge Moscow flatly denies.
Kiev said Ukraine's interim Foreign Minister Andriy Deshchytsya told his Russian counterpart Sergei Lavrov by telephone on Saturday to "stop the provocative activities of Russian special services in the eastern regions of Ukraine."
But Moscow said Lavrov firmly rejected the accusation and "noted that similar claims... have been made by Washington, although we still have not been presented with any concrete proof."
Russia on Friday warned that it would boycott Thursday's Geneva talks should Ukraine try to regain control of the seized buildings through force.