The new Sri Lankan president has finally admitted the 20,000 missing Tamils who vanished during the nation's civil war are dead.

Gotabaya Rajapaksa - who was then defence secretary - led government troops to victory over Tamil soldiers, but his forces were accused of carrying out mass disappearances and executions.

It is the first time the government has admitted its complicity despite the conflict ending in 2009. The move crucially comes as he is about to introduce legislation granting immunity to those who carried out abuses, according to local media reports.

Mr Rajapaksa made the announcement during a meeting with a United Nations envoy in Colombo, the country's capital, and has said official death certificates will be issued.

He said the admission would bring closure to families and he hoped Tamil politicians would not use it as an opportunity to cause unrest.

Sri Lanka's bloody civil war began in 1983 and raged for 26 years, claiming an estimated 100,000 lives.

It was fought along ethnic and religious lines and ended with victory for the Buddhist Sinhalese-majority government at the expense of the Hindu Tamil-minority which was fighting for independence.