Prague - The opposition Social Democratic Party issued a shockingly heavy blow to Prime Minister Mirek Topolanek in the Czech Republic's regional and Senate elections, final results showed Saturday. 

As a consequence Topolanek's position as a party leader and possibly as a premier looked shaky just 10 weeks before his country takes over the European Union's rotating presidency. 

The Social Democrats took all 13 regions where voting took place, their first such success since 2000 when regions came to existence, the Czech Statistical Office said. 

"The voters want change," Social Democratic leader Jiri Paroubek told the public broadcaster Czech Television. 

Topolanek's right-wing Civic Democratic Party has governed in 12 of those regions for the last four years. 

Prague, officially also a region, elects its government in municipal elections that last took place in 2006. 

The Social Democrats also did well in the Senate election, in which voters were picking 27 of 81 senators. 

The party won one seat and is headed for a runoff next Friday and Saturday in 25 districts, leading in 19 of them. 

An overwhelming Social Democratic victory in the upper house could mar US plans to build a missile defence radar on Czech soil. 

"I would like to congratulate the winner ... this is a defeat," Topolanek said on Czech Television, calling the loss "a toll for governance". 

The Topolanek-led centre-right coalition government has introduced several unpopular belt-tightening measures such as direct fees in healthcare, for which analysts expected him to pay dearly in the vote. 

The unexpectedly heavy losses could bring down Topolanek, who was defeated for the first time since taking over party leadership in 2002. 

Paroubek reiterated his party's intention to call for a vote of no confidence on Wednesday. 

The Civic Democratic Party congress, which may issue Topolanek a stern report card for the loss, is planned for December. 

"In the darkest nightmares I have not expected such result," said Mayor of Prague Pavel Bem, Topolanek's rival in the Civic Democratic Party. He said that party leaders should resign at the congress. 

Topolanek now hopes to mitigate the loss in the Senate election runoff next week. 

Twenty Civic Democratic candidates made it to the second round, 19 of whom will face Social Democratic challengers. (dpa)