Berlin's mayor Klaus Wowereit has announced he is to step down after more than a decade in office, amid an ongoing row over the construction of Berlin's new airport.

For years, Wowereit had enjoyed popularity far beyond the capital's borders, not least thanks to a deft turn of phrase and considerable fearlessness in the face of the tabloid media. "I'm gay and that's OK," he casually remarked in the runup to his election in 2001, becoming the first high-profile German politician to declare his homosexuality.

Another snappy phrase, his 2003 description of Berlin as "poor but sexy", summed up his achievement in reinventing the formerly divided city as Europe's capital of cool, helping to attract tourists and investors from across the globe.

On Tuesday, Wowereit said at the press conference called to announce his departure that he was leaving in response to increased speculation about his future from within his own Social Democratic party ranks. He said he had originally wanted to announce his intention in June, "but then we won the World Cup". He is to leave office on 11 December.

"Wowi" had been rumoured in 2009 as his party's candidate to run against Angela Merkel in the German federal elections, but in recent years his popularity levels have plummeted dramatically, mainly due to the ongoing delay of the Berlin Brandenburg airport.

Originally scheduled to open in 2010 but now slated to be finished in 2016, billions over-budget, the project has raised serious questions over Wowereit's economic competence. In his statement, he described it as his "greatest defeat".

In May, Wowereit's plan for a new central library on the disused Tempelhof airfield was rejected by the locals in a referendum; his enthusiasm for bringing the Olympic Games to the German capital in 2024 have been mainly met with ridicule.

Earlier this year, many had called for Wowereit's resignation after Berlin's culture secretary Andre Schmitz, a close ally, resigned in a tax evasion scandal that reflected badly on the mayor.

Wowereit's departure opens up the possibility that after becoming the first German city with an openly gay mayor, Berlin could become the first German city with a Muslim mayor: Social Democrat Raed Saleh, who moved to Berlin from Palestine as a small boy, has become one of the first politicians to throw his hat into the ring.

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