Gunmen have seized a police station in a Ukraine town amid sieges of major government buildings in the country\’s east by pro-Russian separatists.
Police said the gang fired shots and used stun grenades to seize the offices in Sloviansk, near the Russian border.
Interior Minister Arsen Avakov called the gunmen "terrorists" and said special forces would repel the attack.
Pro-Russian protesters have taken over government buildings throughout eastern Ukraine. Kiev says the unrest is being orchestrated from Moscow.
Protesters in the eastern city of Donetsk, 130km (80 miles) from Sloviansk, have been occupying government buildings for days and demanding a referendum on becoming part of Russia.
Regional police spokesman Ihor Dyomin described how armed men were bussed to the police station in Sloviansk.
"Six or seven unknown persons got out. They fired several shots in the air and attempted to storm the police department," he said.
He added that "people in camouflage uniform" and with weapons" were inside the building.
Ukraine\’s prime minister has told leaders in the country\’s restive east that he is committed to allowing regions to have more powers, after a 48-hour ultimatum given to pro-Russian separatists passed without progress in a crisis that threatens the country\’s unity.
He is holding talks with regional leaders in Donetsk, where activists demanding self-rule are holding a big government building.
It is not clear if Arseniy Yatsenyuk\’s offer will satisfy the separatists.
In Donetsk, Yatsenyuk urged regional leaders to tell locals that the Kiev government would ensure security and economic progress in the east, Interfax news agency reports.
"In the framework of the changed constitution, we will be able to satisfy specific requests of every single region," he pledged.
Yatsenyuk pledged that the Russian language would keep its official status in the region, in parallel with Ukrainian.
Yatsenyuk is also expected to travel to another eastern city, Dnipropetrovsk, which has also seen protests.
The government had offered amnesty for those who surrender but initially threatened to use force if the buildings were not cleared by Friday morning.
There were no signs the government was following through on its threat to forcibly vacate the buildings. Neither was there evidence protesters were about to surrender.
NATO on Thursday released aerial photographs showing what it says are 40,000 Russian troops, along with tanks and aircraft massed near the Ukrainian border.
The imagery released to news outlets, follows repeated Russian assurances the deployment is no cause for alarm.
On Friday, Russian Foreign Minister Sergei Lavrov said he is ready for four-party talks on Ukraine with the U.S., the European Union and Kyiv.
But he said in order for tensions to be reduced, the West should stop its efforts to "legitimize" Ukraine\’s pro-Western leaders.
Ukraine\’s current government came to power following the so-called "Euromaidan" protests that forced the country\’s pro-Russian leaders from power in February.
A month later, Moscow proceeded to annex Ukraine\’s Crimean peninsula, a move that prompted Washington to impose sanctions on Russia.
The U.S. is threatening to impose more economic penalties if Russia does not pull back its troops from the border.
A White House statement on Thursday said the U.S. and its allies are "prepared to meet further Russian escalation with additional sanctions."
At the World Bank/IMF spring meetings in Washington Thursday, U.S. leaders also threatened more sanctions against Russia.
U.S. Treasury Secretary Jack Lew told his Russian counterpart he could expect "significant" sanctions in the event of further escalation.
Language is a highly sensitive issue in eastern Ukraine, where ties with Russia are strong.