Berlin  - With a week to go before Germany's general election, the leader of the centre-left Social Democrats (SPD) accused Chancellor Angela Merkel of weak leadership Saturday.

Christian Democrat (CDU) leader Merkel has stated her desire to dump the weakening SPD as a coalition partner, but neither has been highly aggressive to the other in campaigning.

In his most trenchant attack yet, SPD leader Franz Muentefering charged, "Merkel has undermined the authority of the chancellorship and of cabinet."

Speaking to a Sunday newspaper, the Frankfurter Allgemeine Sonntagszeitung, he said she had shown weakness by allowing the CDU's Bavarian sister party, the Christian Social Union (CSU), to defy compromises agreed in cabinet.

"It was a big weakness of Merkel that she did not bang on the table," said Muentefering.

The party's deputy leader, Foreign Minister Frank-Walter Steinmeier, is lead candidate in the election and seeking the chancellorship. Muentefering said he was not seeking any cabinet portfolio himself.

Surveys indicate that Merkel's CDU and the CSU will emerge as the biggest bloc, but not win a majority in the September 27 election.

Most interest focusses on whether a small pro-business party, the Free Democrats (FDP), can win enough seats to scramble into government, or whether Merkel will be constrained to seek a new coalition with the SPD.

Muentefering said Merkel ruled like a driver of a dodgem car who did not want to collide.

"Never crashing, perfect at avoiding, always driving in a circle, and not getting anywhere" he said. "She does not want to shape things, just get re-elected."

The newspaper released his remarks to other media before it went to press.

The Free Democrats were meanwhile set to raise the stakes, with sources telling the German Press Agency dpa that FDP leaders were drafting a commitment in writing that the party would not be available for any coalition with the SPD.

On Friday, Merkel had requested the FDP to make an exclusive promise to support the CDU in order to reassure centre-right voters.  dpa