Mauritania's main opposition leader has been arrested - hours after the president won a third term in office.
Mr Haidalla briefly went into hiding following his earlier arrest
Mohamed Khouna Ould Haidalla, detained briefly before the poll on suspicion of plotting a coup, was taken by police from his headquarters, said an aide.
Veteran leader Maaouiya Ould Taya beat off five other candidates to win 67% of the presidential vote.
Opposition candidates have called for a re-run of the vote, alleging massive fraud - a charge the government denies.
Mr Haidalla had gone into hiding on Friday after polls closed, but reappeared a day later saying he would fight on.
Later on Saturday, he and two other leading opposition candidates called on the population to react to what they called widespread fraud or risk a descent into civil war.
Witnesses say police surrounded his campaign headquarters during the night, and waited until dawn to take him away.
"He was arrested... the police surrounded the building and around 6am (0600 GMT) they stormed it and took him away," said Mr Haidalla's legal adviser, Diabira Maroufa.
Mr Taya - who has been in power since 1984 - won 64% of the vote cast on Friday, according to the Interior Ministry.
President Taya has been elected through the ballot box since 1984
His nearest challenger, Mr Haidalla - himself a former leader - took 19% of the votes.
Police arrested the opposition contender on the eve of polling on suspicion of planning a coup d'etat.
He was provisionally released just hours before voting began but the authorities warned he could be re-arrested at any moment.
Following the announcement of the result on Saturday, Mr Ould Taya's supporters took to the streets of the capital Nouakchott - waving scarves, sounding horns, holding up posters of the leader and cheering.
Many streets were blocked off by the army, and armed police units patrolled the town. Security forces stepped up checkpoints around the presidential palace.
Foreign observers were not invited to monitor the elections, and polls were organised by the interior ministry, which has rejected fraud allegations.
Ould Taya, president and pro-West - 66.69%
Ould Haidalla, Islamist and ex-president - 18.73%
Ould Daddah, half-brother of first president - 6.89%
Ould Boulkheir, first slaves' descendent candidate - 5.3%
Moulaye El Hacen Ould Jied - 1.48%
Aicha Mint Jeddane, first woman candidate - 0.47%
Turnout - 60.83%
Source: Interior Ministry
The results must be validated by the constitutional council within the next 10 days.
President Taya sought re-election six months after the army put down a coup attempt.
He seized power in 1984 in a coup from Mr Haidalla, who was himself put in office by a coup in 1980.
Allegations of fraud and opposition boycotts surrounded Mr Taya's election wins in 1992 and 1997.
New York-based Human Rights Watch warned in September of a "climate of harassment of opposition members" following the arrest of several opposition activists and Islamists.
An Islamic state, Mauritania is nevertheless one of the handful of Arab states to recognise Israel and President Ould Taya has pursued an alliance with the United States.