Mohamed Ould Abdel Aziz, who toppled Mauritania's first democratically elected leader in a military coup last year, was on Wednesday sworn in as president of the Saharan country after winning an election last month, Reuters reported.
Defeated opponents have denounced the poll as a fraud, but France said it was ready to re-engage with the Islamic state, which has pledged to make the fight against al Qaeda a policy priority.
"With this election, Mauritania has become not only respectable again, but also become once again for France a key partner in the region," French Minister for Cooperation Alain Joyandet told reporters in the capital Nouakchott before the ceremony.
"President Aziz is particularly sensitive to the question of security and the fight against the terrorist threat," he said, urging cooperation between Mauritania and Mali in this area.
Both Mauritania and neighbour Mali have been the scenes of al Qaeda attacks, the former most recently when the group's North Africa wing claimed responsibility for the shooting of an American aid worker in Nouakchott in June.
Speaking before several thousand supporters who attended the swearing-in ceremony in Nouakchott's Olympic Stadium, Aziz pledged to fight corruption and uphold the rule of law.
Former colonial power France is one of Mauritania's biggest partners in both trade and aid. In 2007 it set aside 93 million euros ($134 million) in a four-year aid package, only 30 percent of which has so far been paid. Joyandet said France would now consider releasing the rest of the funds.
"In the coming months, cooperation will be restarted and we will re-examine development priorities," Joyandet said.
The European Union suspended aid payments to Mauritania in protest at the military coup last August, but has indicated it may be willing to restart cooperation.
While the international response to the election appears positive, domestic opposition to Abdel Aziz and the manner in which he won 52.6 percent of the vote with which he claimed the election, rumbles on.
The National Front for the Defence of Democracy (FNDD), a political coalition which has campaigned for Abdel Aziz to step down since he seized power last year, said it would not participate in the investiture ceremony, which was attended by the heads of state of neighbouring Senegal and Mali.
"The election of July 18 was neither free, nor democratic, nor transparent," the FNDD said in a joint statement with opposition party the Assembly of Democratic Forces (RFD) on Wednesday.
Candidates who stood against Abdel Aziz appealed last month to the constitutional court to annul the result, citing evidence they said would prove the vote was not conducted fairly, but the court dismissed that claim and upheld the poll result.
"This election is a coup d'etat legalised by fraud," said Ely Ould Mohamed Vall, a former head of state who stood in July's election, winning less than 4 percent of the vote.
"As it does not have domestic legitimacy, it will not have international legitimacy," he said.