KIEV, May 4 - Pro-Russian militants stormed a Ukrainian police station in Odessa on Sunday and freed nearly 70 fellow activists as the country's leaders lamented a police force they said was widely undermined by graft or collaboration with separatists, Reuters reported.

Militants chanted "We will not forgive!" and "Russia!" as they smashed windows and broke down the gate at the compound two days after over 40 pro-Russian activists died in a blaze at a building they had occupied after clashes with pro-Kiev groups.

Odessa police said 67 activists were allowed to walk free.

Some officers were offered the black and orange St. George's ribbon, a Russian military insignia that has become a symbol of the revolt, and were cheered by the crowd of several hundred.

Prime Minister Arseniy Yatseniuk, speaking in the Black Sea port, was pointedly critical of the Odessa police: "If the law enforcement system in Odessa had worked not exclusively on the 'Seventh Kilometer' and had protected people, then these terrorist organizations would have been foiled," he said.

The Seventh Kilometer is an open market on the edge of Odessa, associated in the popular consciousness with the corruption and black market business that have blighted Ukraine's 23 years of post-Soviet independence.

Addressing hundreds of supporters of the Kiev authorities who gathered near the site of the blaze late on Sunday, newly appointed police chief Ivan Katerinchuk promised to bring those behind Friday's deaths to justice, whatever their allegiance: "Like you, I want to restore law and order to Ukraine," he said.

Friday's clashes were the deadliest since Moscow-oriented president Viktor Yanukovych was forced to flee in February and pro-Russian militants launched uprisings in the industrial east. They also marked the first serious disorder far to the west of those eastern areas, heralding possible trouble for Kiev.

Friday's deaths occurred after running clashes, involving petrol bombs and gunfire, between supporters and opponents of Moscow on the streets of Odessa, where the majority of people speak Russian. The pro-Russian activists were trapped in a building as it burned down.

Acting President Oleksandr Turchynov said separatists had met resistance in Odessa but that police forces in the eastern Luhansk and Donetsk regions, focus of support for pro-Russian militants, were in disarray in the face of rebellion.

"In these regions ... there are whole structures working together with the terrorists," Turchynov said in a television interview, employing the term Kiev applies to anti-Kiev militants who have set up strongpoints in a string of eastern towns. "This is a colossal problem."

Turchynov said Russian special forces were working with success to destabilize Ukraine, helped by "guest stars from Transdniestria" - a breakaway territory in eastern Moldova, 50 km (30 miles) from Odessa, that hosts a Russian military base.

NATO commanders have warned that Russia might hope to control a swathe of southern and eastern Ukraine, including the annexed Crimea, all the way to the border with Transdniestria.

Outright civil war in Ukraine and the division of a country the size of France would have serious implications for countries around, not least for Russia and for NATO states bordering it.

As rebellion simmered, questions were raised about the ability of the army as well as police to confront insurgents. (rt/ez)