"The coup attempt failed, loyal forces are still controlling all strategic points," said Army Chief of Staff General Prime Niyongabo in a statement broadcast on state radio.
A Reuters witness reported a journalist at the state broadcaster had said there was still heavy gunfire being heard around the state television and radio station in the capital on Thursday morning. Another witness said loud blasts were heard in the capital.
The witness said two private radio stations and a television station were attacked by unknown men in police uniforms. The two stations were among those that carried Major General Godefroid Niyombare's announcement on Wednesday that he had sacked Nkurunziza.
Neither Niyombare nor his spokespeople were immediately available to comment.
With President Nkurunziza having gone to Tanzania to discuss the crisis with East African leaders on Wednesday, the presidency dismissed the declaration by Niyombare, who was fired as Nkurunziza's intelligence chief in February, saying on Facebook that the coup had been "foiled".
Late on Wednesday night, Nkurunziza's whereabouts were unclear.
A Tanzanian official said he had not attended the talks in Dar es Salaam, and had left to return to Burundi. But Niyombare said the capital's airport and all border crossings were closed.
The East African leaders condemned the bid to oust him and called for a return to "constitutional order".
Late on Wednesday, continental body the African Union condemned the attempted coup.
"The chairperson condemns in the strongest terms today's coup attempt in Bujumbura, calls for the return to constitutional order and urges all stakeholders to exercise utmost restraint," AU Commission chairwoman Nkosazana Dlamini Zuma said in a statement.
Activists say more than 20 people have been killed in weeks of protest against Nkurunziza's re-election bid, plunging Burundi into its worst crisis since an ethnically fueled civil war ended in 2005.
The United Nations said more than 70,000 Burundians had fled to neighboring states in a region with a history of ethnic fighting.