NOUAKCHOTT, Mauritania – A military junta overthrew Mauritania’s American-allied president while he was abroad yesterday, prompting celebrations in this oil-rich Islamic nation that looked increasingly to the West amid alleged threats from Al Qaeda-linked militants.

The junta promised to yield to democratic rule within two years, but African leaders and America were quick to condemn the coup, declaring that the days of authoritarianism and military rule must end across the continent.

President Taya, who himself seized power in a 1984 coup and dealt ruthlessly with his opponents, was out of the country when presidential guardsmen cut broadcasts from the national radio and television stations at dawn and seized a building housing the army chief of staff headquarters.

Mr. Taya, who had allied his overwhelmingly Muslim nation with America in the war on terrorism, refused comment after arriving yesterday in nearby Niger from Saudi Arabia, where he attended King Fahd’s funeral.

The State Department joined the African Union in calling for the restoration of the government.

“We call for a peaceful return for order under the constitution and the established government of President Taya,” a State Department spokesman, Tom Casey, said in Washington, adding that America was reaching out and talking to officials from the government.

He also said the American Embassy in Nouakchott was open but Americans were advised to stay home to ensure their safety. There are 200 to 300 Americans in the country, mostly aid workers and Peace Corps members, according to American officials.

The American military has sent special operations troops to train Mauritania’s army, most recently in June as part of efforts to deny terrorists sanctuary in the under-policed Sahara desert region.

The junta identified itself in a statement on the state-run news agency as the Military Council for Justice and Democracy. “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,” the statement said.

The junta said it would exercise power for up to two years to allow time to put in place “open and transparent” democratic institutions.

Oil recently was discovered in reserves offshore, and Mauritania is expected to begin pumping crude for the first time early next year, but industry analysts said the coup was unlikely to significantly affect global oil prices.

Islamic leaders in the impoverished nation of 3 million have led the opposition to Mr. Taya, criticizing him for building close ties with Israel. Mauritania opened full diplomatic relations with Israel six years ago. The Israeli Embassy in Mauritania was operating normally, although security had been tightened, a Foreign Ministry spokesman, Mark Regev, said in Israel.

After the coup was announced, hundreds of people celebrated in the city center, saluting soldiers guarding the presidential palace, clapping and singing slogans in Arabic against Mr. Taya.

Mr. Taya had survived several coup attempts, including one in 2003 that led to several days of street fighting in the capital. After that, he jailed scores of members of Muslim fundamentalist groups, and accused the army of plotting to overthrow him. His government also has accused opponents of training with Al Qaeda-linked insurgents in Algeria.

A June 4 border raid on a remote Mauritanian army post by Al Qaeda-linked insurgents sparked a gun battle that killed 15 Mauritanian troops and nine attackers. Algeria’s Salafist Group for Call and Combat claimed responsibility, saying the attack was “in revenge for our brothers who were arrested in the last round of detentions in Mauritania.”

This sparsely populated nation on the northwestern edge of the Sahara had been strictly controlled by Mr. Taya, who tried to legitimize his rule in the 1990s through elections the opposition says were fraudulent.