BBC NEWS - Mauritanian soldiers have seized control of the state radio and television station and main routes in the capital, Nouakchott.
Presidential guards are said to have blocked off access to the presidential palace and gunfire has been heard, but it is unclear if it is a coup attempt.
A plane carrying President Maaouiya Ould Sid Ahmed Taya has landed in Niger's capital, Niamey, officials say.
Rebel soldiers came close to toppling him in June 2003.
The government says it foiled two more attempts in 2004.
Correspondents say it is unclear if Wednesday's events signal a coup - or an attempt to prevent one.
A Mauritanian journalist told Al-Jazeera TV that there had been no official information from the authorities or other parties.
A diplomat told Reuters news agency it could be a coup attempt, but it was unclear who was involved.
"We don't know whether it is something that has succeeded or failed," said the British honorary consul in Nouakchott, Sid Ahmed Abeidna.
Troops on streets
Presidential guards moved into state radio and television buildings from 0500 GMT, AFP news agency reports.
State media broadcasts have been cut.
An AFP journalist in the city says that military vehicles equipped with heavy weaponry and anti-aircraft guns have been deployed.
Soldiers have taken up position on the streets.
Some reports say troops have also taken control of the city airport and a key army building.
Gunfire rang out briefly near the presidency building.
"I saw scared people running away. Civil servants have all left their offices," a witness told Reuters news agency.
A BBC correspondent in the city says there are rumours that senior army officers have been arrested.
Sidi El Moctar Cheiguer says he has not heard of any violence since the gunshots.
The capital is calm and people are going about their business normally, our correspondent says.
President Taya had been out of the country attending the funeral of Saudi Arabia's King Fahd.
He took power in a bloodless coup in December 1984 and has been re-elected three times since.
Correspondents say he later made enemies among Islamists in the country, which is an Islamic Republic.
Critics accuse the government of using the US-led war on terror to crackdown on Islamic opponents.
Mr Taya has also prompted widespread opposition by establishing links with Israel.
Earlier this year, nearly 200 people, including former President Mohamed Khouna Ould Haidallah, were put on trial for a series of alleged coup plots.
Mauritania is deeply divided between three main groups - light-skinned Arabic-speakers, descendents of slaves and dark-skinned speakers of West African languages.
Wednesday, August 03, 2005
Coup in Mauritania
Coup in Mauritania