UNITED NATIONS - UN Secretary-General Ban Ki-moon on Saturday voiced his deep concern over the deteriorating situation in eastern Ukraine.

"The secretary-general is deeply concerned about the deteriorating situation in eastern Ukraine?and the growing potential for violent clashes," said a statement issued here by Ban's spokesman Saturday night.

"The secretary-general stresses that further disturbances will not serve the interests of any side," the statement said.

A new wave of unrest erupted in Ukraine's east last weekend, when pro-Moscow activists seized several government buildings in the cities of Donetsk, Lugansk and Kharkov, demanding a referendum on autonomy and closer ties with Russia.

Earlier Saturday, about a dozen gunmen seized a state security building and a police station in Slavyansk, a town about 100 km north of Donetsk in eastern Ukraine.

The armed men initially occupied the police station, where they seized at least 400 handguns and 20 automatic weapons, Ukraine police said in a statement.

The attack on the police station was followed up with the storming of the state security building. Casualties and hostages remain unknown.

Ukraine Interior Minister Arsen Avakov said on his Facebook account the attack was led by "armed men in camouflage fatigues" and he vowed a severe response.

In the statement, the secretary-general "appeals to all sides to work towards calming the situation, adhere to the rule of law and exercise maximum restraint."

"He calls again for urgent and constructive dialogue to de-escalate the situation and address all differences," said the statement.

"The United Nations stands ready to continue to support a peaceful resolution to the current crisis facing Ukraine," it added.

On March 18, Russian President Vladimir Putin and Crimean leaders signed a treaty to make the southern peninsula part of Russian territory after almost 97 percent of Crimean voters backed secession from Ukraine in a referendum.

Kiev has rejected the referendum and Crimea's integration into Russia, saying it was unconstitutional.

Pro-Russian demonstrators announce Kharkov's independence	?Ukraine moves to end separatist grip on eastern town