Tension mounted in Mauritania, the final day of campaigning for the west African state's presidential election, as a leading opposition candidate was accused of seeking to "sow disorder" two days ahead of the vote. The accusation came after police raided the home of opposition candidate Mohamed Khouna Ould Haidallah, arrested two of his sons and used tear gas to break up a march he and two other opposition candidates had called to protest at the police operations. The campaign manager for longtime President Maaouiya Ould Taya charged that Ould Haidallah, a former head of state who was ousted in a coup by Ould Taya in 1984, was himself planning a coup in case his rival won Friday's election in suspicious circumstances. Campaign manager Hamoud Ould M'Hamed handed out a five-page document to journalists which he said contained the alleged "coup plan", under which the opposition would set up an alternative government in case of a disputed re-election victory by Ould Taya. Ould M'Hamed said the so-called "Grab Plan" set out a number of variations depending on the outcome of the six-way poll. He accused Ould Haidallah of "seeking to sow disorder and sabotage the institutions of the republic". The Senegal-based African Assembly for the Defense of Human Rights (RADDHO) said it was "deeply concerned" over the police operations against Ould Haidallah and called for the release of his sons. Earlier Wednesday, several hundred people who had gathered to protest in support of Ould Haidallah dispersed without incident after police used tear gas to prevent what they said was an unauthorized march. Ould Haidallah and two other opposition candidates who had planned to march in solidarity with him had not yet arrived at the departure point in central Nouakchott when the police moved in. The two other candidates were Ahmed Ould Daddah, the half-brother of the late Moktar Ould Daddah, Mauritania's first president who died last month, and Messaoud Ould Boulkheir, the first descendant of slaves to run for president here. Police said they had searched Ould Haidallah's house as well as those of "some of his supporters and some mosques" and that two guns had been seized as "a precaution". They said they had been informed of "the determination of extremist groups ... to dispute with violence any result of the election that is not favorable to them". On Tuesday Ould Haidallah's eldest son, Sid'Ahmed, was arrested and accused of "engaging in intimidating and threatening acts with the aim of infringing public security", according to a police statement. Sources close to the candidate said Wednesday that another son, Sidi Mohamed, was arrested on the same charges. The election comes six months after an attempted military coup was violently quashed in the former French colony. Ould Haidallah's spokesman, Ely Ould Sneiba, said that if Ould Taya was re-elected on Friday his victory would be recognized only if the vote took place "without fraud and in a transparent manner". The New York-based group Human Rights Watch warned in September of a "climate of harassment of opposition members" in Mauritania and voiced fears over the fairness of the upcoming vote. It noted the arrests of dozens of religious leaders, opposition politicians and social activists on allegations of involvement in "terrorist" activities. The government has not invited foreign observers to monitor the poll. The president's spokesman, Mohamed Vall Ould Bellal, late Tuesday told reporters that Ould Taya would accept the outcome of the vote, in which two other minor candidates are also standing, "without condition", adding that this acceptance would be "a decisive and positive turning point" for the country. The election will go to a second round two weeks later if none of the candidates takes more than 50 percent of the vote on Friday. Ould Taya has won two elections since he ousted Ould Haidallah in 1984 -- in 1992 amid fraud charges and again in a 1997 vote largely boycotted by the opposition. The two other candidates in Friday's vote are Moulaye el Hacen Ould Jied, who picked up less than one percent of the vote in 1997, and the first woman contender, Aicha Mint Jeddane. **PHOTO CAPTION*** Ahmed Ould Daddah, Mauritanian presidential candidate, the half-brother of Mauritania's late first president Moktar Ould Daddah, salutes supporters at his party headquarters in Nouackchott. (AFP/File/Georges Gobet)