State radio had reported that a group calling itself the National Patriotic Youth Front tried to overthrow the government of President Pierre Buyoya.
Buyoya, leader of the Tutsi-dominated government - and a key figure in the country's seven-year-old civil war - was in Gabon for peace talks with opposition Hutu rebels. He took power in a coup in July 1996, promising to end the fighting that has left more than 200,000 dead.
Members of a previously unknown group, The National Youth Patriotic Front, had taken over the state-run radio and announced that "the government, which is killing people, is over, and the government of Buyoya is over now." They are opposed to any negotiations with the Hutu rebels.
However, a government spokesman loyal to Buyoya said that the coup had been put down. In a statement on the independent Bonesha radio, the army said junior officers in the Tutsi-dominated army were surrounded inside the state radio offices.
"The mutineers have started to surrender to loyalists," Colonel Augustin Nzabampema said, adding there appeared to be about a total of 40 people involved in the attempted coup.
In South Africa, Nelson Mandela said Buyoya had told him that he was still in charge.
"As far as President Pierre Buyoya's office is concerned, there is no coup in Burundi. Government activities have not been affected but some armed men are occupying the radio station," Mandela's spokeswoman Zelda la Grange said.
Although Hutus make up the majority of Burundi's population and dominate the national assembly, a 1996 agreement legitimized Buyoya's presidency. The Tutsi minority controls the government.
The civil war began in October 1993, when Tutsi paratroopers assassinated the country's first democratically elected president, Melchior Ndadaye, a Hutu.
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