Former left-wing guerrilla fighter José Mujica has taken the lead in Uruguay's presidential elections, but has failed to secure more than 50 percent of the vote needed for an outright victory.

Mr Mujica's lead is expected to widen as returns come in from the capital Montevideo, a stronghold of his ruling socialist coalition Frente Amplio or Broad Front, but he is unlikely to capture more than half the vote. In that case, he will face his conservative rival and former president Luis Alberto Lacalle in a run-off on 29 November.

Mr Lacalle, who heads the Nationalist Party, has made a political comeback with around 30 percent of the votes. His 1990-1995 presidential term ended with corruption accusations involving several of his top aides. The current president of Uruguay, Tabaré Vázquez, cannot stand for election, as he has held office for five years, the maximum permitted by the Uruguayan constitution. President Vazquez is also a member of Broad Front.

As well as presidential and congressional elections, voters took part in a referendum. That proposed revoking a law which gives immunity to former security officials accused of human rights abuses during Uruguay's period of dictatorship between 1973 and 1985.