U.S. Ambassador Joseph LeBaron and his French counterpart were called to a meeting in the capital, Nouakchott, with members of a group calling itself the Military Council for Justice and Democracy.
Headed by national police chief Colonel Ely Ould Mohammed Vall -- formerly a close confidant of the ousted president -- the 17-member council said it would rule the sparsely populated desert nation for up to two years.
"The armed forces have unanimously decided to put an end to the totalitarian practices of the deposed regime under which our people have suffered much over the last several years," it said in a statement posted on the official government website.
President Maaouiya Ould Sid'Ahmed Taya was toppled while abroad, having traveled to Saudi Arabia for King Fahd's funeral. He is currently in the Central African nation of Niger.
The coup, which apparently occurred without loss of life, has been widely condemned by the international community, and the 53-nation African Union said it was suspending Nouakchott's membership "until the restoration of constitutional order."
Mauritania, a former French colony with a population of less than three million, straddles Arab North Africa and black West Africa. It has endured several coups and attempted coups since becoming independent in 1960, including the one that bought Taya to power in 1984.
Taya eventually allowed multiparty elections in 1992, winning them in 1992, 1997 and again in 2003, when opposition groups claimed he had used fraudulent means.
Although among the world's poorest countries, Mauritania is poised to benefit from the exploitation of offshore oil and natural gas reserves.
According to the State Department, relations with the U.S. were "cordial" during the early years of independence, but then were severed by the Islamic country for two years as a result of the 1967 Israeli-Arab war.
Ties were "relatively friendly" until the late 1980s, when they soured again as a result of a serious dispute with Senegal, Mauritania's support for Iraqi leader Saddam Hussein before and during the 1991 Gulf War, severe human rights abuses by the military and slavery.
As a result, Washington ended USAID operations and military assistance.
A turnaround in the late 1990s saw the Taya regime turn away from Iraq and towards the U.S., establish diplomatic relations with Israel in 2000 and support the U.S.-led campaign against terrorism after 9/11.
The improved relations brought a return of military cooperation and training programs, with U.S. forces as recently as last June training Mauritanian troops in counter-terrorism operations.
Rights abuses have continued, however, including arbitrary arrest and detentions, as well as restrictions on freedom of speech, the press and assembly, the State Department said in its most recent global human rights report.
After surviving a bloody coup attempt in 2003, Taya jailed scores of opponents, including soldiers and Muslim fundamentalists, accusing some of having ties to the al Qaeda-linked terrorist organization Salafist Group for Call and Combat, based in neighboring Algeria.
The Salafist Group has claimed responsibility for attacks against Mauritanian troops, although some human rights groups accused Taya of using the Islamist threat as a pretext to clamp down on any political opponents.
Israel will be closely watching developments in Mauritania, one of only three Muslim nations to have diplomatic relations with the Jewish state. The other two are Egypt and Jordan.
Taya's stance on Israel was controversial at home and in the wider Muslim world. When Israeli Foreign Minister Silvan Shalom paid a brief visit last March, violent street protests erupted.
Just two weeks ago, Mauritanian foreign minister Mohamed Vall Ould Bellal called on more Arab countries to establish diplomatic ties with Israel and contribute to Middle East peace efforts.
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