The runner-up in Sunday's presidential election in Guinea-Bissau has said he will not participate in a run-off vote.
Former president Kumba Yala has claimed the first round of voting was unfair.
Provisional results from Sunday's poll gave ex-prime minister Carlos Gomez 49% of the vote out of nine candidates. Kumba Yala came in second with 23%.
As Mr Gomez did not win a majority there must now be a run-off vote, but Mr Yala says new voter registration must be done before he will take part.
He told the BBC's Focus on Africa programme: "This election wasn't fair - the numbers were fabricated. We have evidence that [Carlos Gomes] rigged the vote... and we will show them to the authorities."
Foreign electoral observer missions have said Sunday's vote - held to find a successor to president Malam Bacai Sanha who died in January after a long illness - was largely free and fair.
Mr Yala was overthrown as president in a 2003 coup, one in a long line of military coups in the west African state.
The country has also been destabilised by the booming illegal drugs trade from Latin America, which uses it as a staging post for the European market.