One military source in the mining town of Zouerat, 400km west of the site of the attack, said on Sunday that he had heard of 15 soldiers dead and 20 wounded. Other sources spoke of several casualties.
There was no official word on the incident from the government or the army, but a second military source said Mauritanian troops had been put on maximum alert.
The attack took place late on Thursday in the village of Limgheiti, not far from the border with Mali and Algeria.
The desert triangle between the three countries is a haven for smugglers and the United States says it is a training ground for Islamist recruits.
Travellers who came from Limgheiti to Zouerat said gunshots had been heard near the military post on the night of the attack.
They and other sources said the attackers burned some military vehicles and stole others. The army sent reinforcements from the capital Nouakchott, 750km south of Zouerat.
In recent months, Mauritania has arrested about 50 suspected Islamists saying they had links to Algeria's Salafist Group for Preaching and Combat, an al-Qaida ally.
The Islamic republic, which critics say is taking advantage of the US-led "war on terror" to crackdown on opponents, straddles black and Arab Africa.
Maaouya Ould Taya is a staunch
There have been three coup attempts since June 2003. Some of the dissident soldiers wanted for the failed bids to overthrow President Maaouya Ould Taya are still at large.
Taya, who seized power in a 1984 coup, has angered many Arabs in his country by shifting support from former Iraqi president Saddam Hussein to the United States and Israel.
In 1999, Mauritania became only the third Arab League member country to establish diplomatic relations with Israel.
Ahmad Wild al-Wadiyaa, the media chief of the Mauritanian Platform for Reform and Democracy, told Aljazeera that there are three possible explanations behind the attack.
Speaking from Brussels, he said the incident could have been sparked by an internal coup at the military base; that the Knights of Change rebel group may have carried out the operation; or that a foreign "terrorist" group may have been behind it.
"The sole solution to get the country out of this impasse is for all Mauritanian national and political forces to call for the liberation of Mauritania through peaceful and democratic means to get rid of the oppressive regime"
Ahmad Wild al-Wadiyaa,
Mauritanian Platform for Reform and Democracy
He also said that any assault against Mauritanian civilians or military personel should be condemned.
"The sole solution to get the country out of this impasse is for all Mauritanian national and political forces to call for the liberation of Mauritania through peaceful and democratic means to get rid of the oppressive regime", he added.