Ex-rebel leader Jean-Pierre Bemba has accepted defeat in the Democratic Republic of Congo's presidential poll.
Mr Bemba has challenged the election result in court
He said he stood by his complaints against President Joseph Kabila's run-off victory - which were rejected by the Supreme Court on Monday.
But he would participate in a "strong republican opposition in the interests of the nation", his statement said.
International observers said the first democratic elections since independence in 1960 had been broadly free and fair.
The court confirmed the provisional results of the Independent Electoral Commission, with Mr Kabila winning 58% of the vote compared to Mr Bemba's 42%.
It means that Mr Kabila, president since his father's assassination in 2001, will continue to rule DR Congo, which is trying to recover after a bloody five-year war.
Last week, a protest by Bemba supporters outside the Supreme Court led to violence and the court was set alight.
Forces loyal to Mr Bemba were subsequently ordered out of the capital by Mr Kabila.
The results showed a regional divide, with Mr Bemba gaining most votes in the Lingala-speaking west, including Kinshasa, while Mr Kabila won by a landslide in the Swahili-speaking east.
US election observer group the Carter Center said there was evidence of vote tampering on both sides.
But it said neither candidate benefited significantly over the other.
The elections were supposed to draw a line under a five-year conflict in which about four million people died.
The polls were organised under the terms of a 2002 peace deal to end a war that drew in the armies of nine other African countries.
Under the deal, former rebels were supposed to be integrated into the army, but progress has been slow and the three former rebel leaders who are vice-presidents have retained large personal security forces.
The world's biggest peacekeeping force - about 17,000 strong - is in DR Congo to prevent unrest.