Mahfudh walad Ammar, spokesman for Mauritania's police, said in a statement on Tuesday that recent confessions had linked the Islamist leaders arrested on Monday to the Salafist Group for Preaching and Combat (GSPC), based in neighbouring Algeria.
"They sent about 20 people to the GSPC for military training and the first contingent of seven has returned to the country," the police said in its statement.
"These elements have been arrested, the rest of the group is still in GSPC training camps," it said. "The dismantling of this structure has entered a new phase with the arrest on Monday ... of the main leaders of the organisation".
President Muawiya walad Sidi Ahmad Taya angered many Arabs in a nation straddling sub-Saharan and Arab Africa when he shifted support from former Iraqi President Saddam Hussein towards Israel and the United States.
Mauritania became the third Arab League state to establish full diplomatic relations with Israel in 1999. The government has said Israel's foreign minister is due to visit Nouakchott but has given no further details.
Opposition members said Islamic spiritual leader Shaikh Muhammad al-Hasan walad Didu and Mukhtar walad Muhammad Musa, a former diplomat to several Arab states, were arrested on Monday with up to 14 members of the moderate Islamist opposition.
"The regime has started a new repression against a strong current of national opinion probably to please the Israeli foreign minister before his visit to Nouakchott," Islamist leader Muhammad Jamil walad Mansur said.
Mauritania is an impoverished former French colony where power has not changed hands through the ballot box since independence in 1960.
Critics say Taya, who seized power in a 1984 coup, exaggerates the Islamist threat to curry favour with Washington while using it as a justification for stifling opposition.