Sri Lanka's long-time leader Mahinda Rajapaksa has admitted defeat in the presidential election, his office says.President Rajapaksa has dominated politics for a decade, but faced an unexpected challenge from his health minister Maithripala Sirisena.The statement said Mr Rajapaksa would "ensure a smooth transition of power". Official results are not due until later on Friday, but early results indicated that Mr Sirisena was on course to win the 50% needed.He has not yet commented. Mr Rajapaksa, who was seeking a third term in office, is credited by many with ending the civil war in 2009, when troops routed the Tamil Tigers separatist rebels after more than two decades of fighting. But rights groups accused both sides in the war of atrocities, allegations the government denies.Mr Rajakpaksa's press officer said the president "concedes defeat and will ensure a smooth transition of power bowing to the wishes of the people". He added that Mr Rajapaksa had already left his official residence and the new leader would be sworn in later on Friday.