* Confrontation follows offer of top posts to opposition
* Opposition says will keep up demands for early election
* Ukraine's U-turn away from Europe has divided country
By Pavel Polityuk
KIEV, Jan 26 (Reuters) - Police clashed with protesters who blockaded a building in central Kiev on Sunday and the fate of Ukraine's government was up in the air after embattled President Viktor Yanukovich offered opposition leaders key posts.
One of the president's main foes called his offer a "poisoned" attempt to kill off a protest movement in a country plunged into political unrest by Yanukovich's U-turn away from the European Union and toward Russia.
In the latest violence, a few thousand protesters tried to storm an ornate cultural centre where hundreds of security forces were gathered in central Kiev, a few hundred metres from the hub of weeks of opposition protests on Independence Square.
Demonstrators threw stones and smoke bombs while police fired stun grenades and sprayed water into the crowd.
The police and security forces later left the building, its windows shattered, and streamed out through a corridor created by the crowd after an opposition leader, Vitaly Klitschko, arrived at the scene and helped negotiate a solution.
The two-hour, pre-dawn confrontation came after Yanukovich made his biggest concession yet in a two-month-old standoff that has cast Ukraine into crisis, killed at least three people and deepened tension between Russia and the West.
Yanukovich abruptly abandoned plans to sign political association and free trade deals with the European Union in November, pledging instead to improve ties with former Soviet master Russia and angering millions who dream of being in Europe.
Hoping to end protests that threaten to bring the country to a standstill, Yanukovich on Saturday offered former economy minister Arseny Yatsenyuk the post of prime minister. Klitschko, a former international boxing champion, was offered the post of deputy prime minister responsible for humanitarian issues, a statement on the presidential website said.
The presidency linked its offer to the opposition reining in violent protesters. Though the protest movement is largely peaceful, a hard core of radicals have been fighting pitched battles with police away from Independence Square.
EARLY ELECTION
Opposition leaders, whose power base is among protesters massing in the square whose name evokes the independence Ukraine gained in 1991, continued to press for concessions including early elections and the repeal of an anti-protest law.
"We are ready to take on this responsibility and take the country into the European Union," Yatsenyuk was quoted as telling crowds on Independence Square after emerging from talks with Yanukovich. But he added this would entail the freeing of former prime minister Yulia Tymoshenko, who was jailed in 2011.