Shooting has broken out in various parts of the capital of the Democratic Republic of Congo, Kinshasa, in what is feared to have been a coup attempt.
DR Congo is emerging from five years of war
One soldier was killed and two injured as unknown gunmen attacked military installations and a TV station.
"There appears to have been a coup attempt," said UK Ambassador in Kinshasa Jim Atkinson.
The government says the situation is now under control and it appealed to the people to remain calm.
DR Congo is recovering from five years of war, which ended with a peace deal in 2002.
This is the first time since then that fighting has erupted in the centre of Kinshasa, says the BBC's Arnaud Zajtman, reporting from the capital.
Gunfire was heard at around 0330 (0230 GMT).
Information Minister Vital Kamerhe announced on state
television on Sunday morning that armed groups had simultaneously attacked two army posts, a naval base, and Ndolo military airport.
Shells were also dropped on densely populated parts of town, and a private television station also came under attack.
"Rocket-propelled grenades were fired from the direction of the Palais de la Nation [Presidential Palace] in the direction of the president's house and fire returned," said the UK Ambassador in Kinshasa, Jim Atkinson, quoted by Reuters news agency.
Unnamed police officers quoted by AFP news agency said the attackers were former members of the personal guard of the late dictator Mobutu Sese Seko - who was ousted in 1997.
One officer said some of the assailants came overnight from Brazzaville, the capital of the neighbouring Congo Republic across the Congo river.
The attackers have retreated to an area near the ferry landing point outside Kinshasa, they added.
More than 3,000 members of the former guard are currently housed in Brazzaville.
The national radio has stopped broadcasting.
Our correspondent says that by early afternoon there were few people on the streets of Kinshasa.
The UN mission in Kinshasa is getting extra protection
Soldiers riding pick-up trucks mounted with machine guns have taken up position at strategic points - notably near
the headquarters of the UN mission in Congo.
Several arrests have been made and weapons seized, said Mr Kamerhe.
DR Congo - formerly known as Zaire - is emerging from five years of war in which it is thought more than three million people died.
President Joseph Kabila heads a power-sharing government
under peace deals that ended the fighting.