The official spoke on condition of anonymity because he is not an authorized spokesman.
Yahya Ould Kebd, minister of decentralisation in the deposed government said: "His contact with the outside will probably be limited but not banned. The authorities want to reign in his activism".
France's Foreign Ministry said in a statement on Friday that Waqef's arrest was "unacceptable," and that he should be released immediately and unconditionally.
The statement said France supported a proposal by Louis Michel, the EU Development Commissioner, for talks that could result in the suspension of EU aid for Mauritania.
France is the former colonial ruler of Mauritania, which became independent in 1960.
Meanwhile, the World Bank suspended $175 million in aid to Mauritania, a World Bank spokesman said on Friday.
The suspended payments are undisbursed funds from $413 million committed by the World Bank for projects in Mauritania, Eric Chinje, spokesman for the World Bank's Africa Region, said.
The suspension affects some 17 national projects in Mauritania and Mauritania's participation in World Bank regional projects, including rural development, health, education and infrastructure such as road building, he said
"Each time there's political instability there's a price to be paid by the country."
Chinje said a World Bank team of about 24 local and international staff had begun an assessment with donors on the ground, such as the United Nations, "in the wake of the problems in the country, the toppling of the government".