Social Democrat leader Martin Schulz on Friday abandoned his plan to become Germany's next foreign minister as his party descended into open warfare and a coalition deal with Angela Merkel was thrown into doubt.

Schulz's decision came a day after an extraordinary attack by his predecessor as party leader, Sigmar Gabriel, who is also the outgoing foreign minister. Gabriel, apparently angry that he would not remain in charge of the foreign ministry, accused the current party leadership of a lack of respect.

Schulz's move leaves the Social Democrats looking for a new foreign minister and raises new questions about whether SPD members will back the coalition pact agreed by their leaders just two days earlier.

Schulz, the former European Parliament president, had come under heavy pressure from within his party not to take up a ministerial post, as he had previously said he would not to serve in a new "grand coalition" government under Merkel.

"it’s appropriate that my personal ambitions should take a back seat to the interests of the party” — Martin Schulz

But when the new coalition deal was announced on Wednesday, it swiftly became clear that Schulz intended to become foreign minister. On Friday, Schulz bowed to the backlash against his plan.

"I hereby forgo joining the federal government," he said. "At the same time, I sincerely hope that this will end the personnel debates within the SPD."

“We all do politics for the people in this country,” he said in a statement. “So it’s appropriate that my personal ambitions should take a back seat to the interests of the party.”

Merkel has also faced criticism over the deal, with members of her own party accusing her of giving away too many key ministries to the SPD.

U-turn

After last September's general election, in which the Social Democrats sunk to a postwar low of 20.5 percent of the vote, Schulz said the party would not reprise its role as junior partner to Merkel and would instead renew itself in opposition.

That view had wide support in the SPD ranks, with many believing being the junior partner in government was damaging the party's image and future electoral chances.

But Schulz performed a U-turn after coalition talks between Merkel's conservatives, the liberal Free Democrats and the Greens collapsed last November.

Just a few days ago, Schulz seemed to be sitting pretty. Having persuaded the party faithful to let him hold coalition talks, he struck what seemed a good deal for the SPD — keeping the foreign ministry it held in the last government and taking over the finance ministry from Merkel's Christian Democratic Union.

Merkel, meanwhile, was widely seen as a clear loser. In a survey by Civey Institute for Welt published Thursday, almost two-thirds of Germans said Merkel had been weakened by the deal. Even among supporters of the CDU/CSU bloc, only 27 percent thought she had been strengthened.

With a place at the foreign ministry seemingly secured, Schulz said he would quit as leader of the SPD after party members voted on the coalition deal. He suggested his successor should be parliamentary group chief Andrea Nahles.

But then Gabriel struck on Thursday night.

"I have enjoyed carrying out the role of foreign minister. And in the eyes of the public I have clearly carried out my duties very well and successfully," he told Germany's Funke media group.

"It is clear, unfortunately, that the public's regard for my work meant absolutely nothing to the new SPD leadership," he complained.

"What's left is regret at how little respect there is in the Social Democratic Party in our dealings with one another, and how little someone's word counts for," Gabriel said, possibly referring to assurances he had been given that he could keep his post.

Gabriel even seemed to get personal in his remarks about the bearded Schulz. He said his young daughter had told him: "You don't need to be sad, daddy. Now you have more time with us. That's better than being with the man with the hair on his face."