Ruling party candidate Mohamed Ould Ghazouani officially won with 52 percent of Saturday’s vote but opposition leaders have rejected the result.
Ghazouani, a former general, is a close ally of outgoing president Mohamed Ould Abdel Aziz, who stepped down after serving two five-year terms.
The election represents the country’s first democratic transition of power since independence in 1960 but protesters have said the vote was flawed.
Access to websites, social networks and emails remained blocked on Wednesday after being restricted from 1500 local time/GMT on Tuesday, AFP correspondents said.
Armed soldiers have been deployed near the presidential palace and constitutional council in the capital Nouakchott, two days after police clashed with opposition supporters and raided the headquarters of two opposition parties.
The government on Tuesday said it had arrested more than one hundred foreigners, blaming opposition parties for contacts with outside forces seeking to destabilise the country through protests.
The ambassadors of Senegal, Mali and The Gambia were summoned by the foreign ministry and urged to tell their nationals to “refrain” from demonstrations or disturbing the public order.
The conservative Saharan country, with a population of less than five million, has a history of military coups, the most recent in 2008.