Speculation is rife that Renate Künast, head of the Green federal parliamentary party, will stand for election to lead Berlin, after polls put the Greens ahead of the SPD for the first time.
A survey carried out for the daily Berliner Zeitung showed the Greens at 27 percent of the vote, slightly ahead of the SPD which was on 26 percent, a year ahead of the state election.
But Künast would face determined opposition from the SPD, party leader Andrea Nahles told Sunday's edition of the Berlin-based newspaper Der Tagesspiegel.
“Frau Künast would be a competitor against whom we would fight hard,” she told the paper.
She also accused the environmentalist Greens of trying to claim mainstream status from the SPD without being willing or able to take on responsibility for the entire population.
“It is easy to see through this game,” said Nahles. “They want to become strong numerically, without making the effort to create compromises between the interests of different milieus.”
Whoever takes on the office of mayor must work for all the city's people, and find solutions for the whole city, she said.
“The Greens fail there, it is not convincing,” added Nahles.
She said that Wowereit, who has headed a coalition between the SPD and the socialist Left party in the city since 2002, has helped make Berlin the "coolest city in the world."
A recent opinion poll suggested that Wowereit and Künast would both get 40 percent of votes if there was to be a direct election for the capital's mayor.
Künast has not yet made a statement on whether she will challenge him – a decision is set to be made by the end of the year.