Berlin - The outgoing leader of Germany's Social Democrats (SPD), Kurt Beck, weighed into unnamed members within his party Tuesday for "leaking misinformation" to the media, in a statement explaining his unexpected decision to quite as federal chairman.

Beck, premier of the western state of Rhineland-Palatinate, said he had taken the decision after due consideration and "intense self- examination."

Speaking to journalists in the state capital of Mainz, Beck said "deliberate untruths" had been planted in the media about him on Saturday.

"After that it was no longer possible for me to carry out my task in a proper way," he said.

The locally popular SPD leader, premier in the state since 1994 and thus Germany's longest-serving state premier, made clear he would continue to lead both the SPD and the government in the state.

The SPD, the junior partner in Chancellor Angela Merkel's federal "grand coalition," announced Sunday that Frank-Walter Steinmeier, the German foreign minister, would be its candidate for chancellor in next year's general election.

Steinmeier's nomination ahead of Beck to take on Merkel had been widely anticipated and, according to both, had been agreed between them some time ago.

But Beck's resignation came as a bombshell and caused deep dismay on the left of the party, where the trained electrician is regarded as a standard-bearer.

On Monday, national leaders nominated Franz Muentefering, a former leader of the party, to replace Beck as national chairman.

Beck is seen as a "tribune of the people" in the party and is highly regarded on its left wing.

But his indecisiveness over doing a deal with the socialist Left Party in neighbouring Hesse, where inconclusive January elections left the state under the control of Merkel's Christian Democrats (CDU), caused the SPD to plummet to post-war lows in the polls. (dpa)