Judges for a five-million dollar prize recognising African good governance said on Monday they had decided not to award the honour this year.

The Mo Ibrahim Prize for achievement in African leadership is described by organisers as the largest individual annual award in the world, with the winner receiving the five million dollars plus $200 000 a year for life.

It goes to a democratically elected former leader from a sub-Saharan African country who has left office in the last three years and recognises good governance.

But announcing this year's decision, President Ketumile Masire of Botswana said "the prize committee could not select a winner" despite lengthy deliberations.

The board said it could not give the reasons why it did not select someone because of the confidential terms of the decision-making process.

The prize, named after Sudanese-born businessman Mo Ibrahim, was first given in 2007, to former Mozambican president Joaquim Chissano, followed by Festus Mogae, Botswana's former head of state, last year.

South African anti-apartheid icon Nelson Mandela is an honorary laureate.