Participants of a rally welcome men just released from a city police department and who were earlier arrested in recent street battles between pro-Russian and pro-Ukrainian supporters in the Black Sea port of Odessa May 4, 2014.[Photo/Agencies]

ODESSA, Ukraine - Hundreds of pro-Russian demonstrators stormed police headquarters in Odessa on Sunday and won the release of 67 people detained after deadly clashes in the Ukrainian port city.

Ukraine crisis

More than 40 people died in the riots two days earlier, some from gunshot wounds, but most in a horrific fire that tore through a trade union building.

Ukrainian Prime Minister Arseniy Yatsenyuk, who hinted that he saw Moscow's hand in the unrest spreading through southeastern Ukraine, visited Odessa on Sunday to try to defuse the mounting tensions.

Odessa is the major city between the Crimean Peninsula, which Russia annexed in March, and the Moldovan separatist region of Trans-Dniester, where Russia has a military peacekeeping contingent.

Yatsenyuk said all the city's police chiefs had been sacked for not preventing the clashes and ensuing deaths.

Earlier in the day, hundreds of pro-Russian demonstrators gathered in front of the scorched trade union building to honor those who died in Friday's blaze. Some draped a large Russian tricolor flag on the face of the building.

By mid-afternoon, a group of several hundred people marched to the police station to demand the release of fellow activists jailed over their involvement in the unrest. They attacked security surveillance cameras and smashed windows. Shortly after some of them managed to break into an inner courtyard, police yielded to the crowd's demands and released the prisoners.

As detainees emerged from the police station, the crowd cheered.

The Interior Ministry said in a statement that 67 activists had been released. It was not immediately clear whether others were still being held.

Yatsenyuk's visit came as Ukrainian authorities renewed their push to quell a pro-Russian insurgency in the east. Interior Minister Arsen Avakov said in a statement on his Facebook page that an "antiterrorist operation" was being executed in the eastern city of Kramatorsk, the latest flashpoint for unrest.

"The operation was carried out by fighters of the National Guard and the armed forces. The active phase resumed at dawn. We will not stop," Avakov wrote.

Tensions in eastern Ukraine have been escalating since mid-April following an armed confrontation between Ukrainian security forces and pro-Moscow activists, who demand a referendum on autonomy and closer ties with Russia.

Kiev has repeatedly blamed Moscow for inciting the unrest and splitting Ukraine. Russia denies the charges.

In Moscow, Russian Deputy Foreign Minister Grigory Karasin said Sunday that Kiev needed help to establish a dialogue with pro-Russia activists in southeastern Ukraine.

"It appears that without external help the Kiev authorities are not capable of establishing such a dialogue," Karasin told Rossiya-24 television.

He said steps would soon be taken to bring a dialogue about, without giving further details.