The head of Burundi's army said on Thursday that an attempted coup had failed and forces loyal to President Pierre Nkurunziza were in control but heavy gunfire in the capital suggested the battle for power was not yet over.

Army Chief of Staff General Prime Niyongabo's announcement came a day after another general said he had sacked Nkurunziza for seeking an unconstitutional third term in office, developments that have alarmed neighboring governments.

Heavy gunfire was heard coming from the direction of the state broadcasting headquarters, a Reuters witness said. State radio and television both went off air. The state broadcaster is seen as a vital asset for both sides to reach the population.

It was difficult to determine who was now in control of the capital, with periods of relative calm broken by bouts of heavy gunfire. A Reuters witness saw one dead soldier lying near the Interior Ministry. Nearby troops said he was a coup supporter.

Shortly before transmission stopped, the president praised loyalists and offered amnesty to soldiers opposing him.

"I condemn that group of coup plotters," he said in a radio broadcast. "I thank soldiers who are putting things in order, and I forgive any soldier who decides to surrender."

Nkurunziza, who sparked more than two weeks of protests by saying he would seek another five years in office, was in Tanzania for an African leaders meeting on Wednesday when the attempt to topple him was announced.

There was no official confirmation of his whereabouts, but Tanzanian sources said he was at a secure location in Dar es Salaam.

"The coup attempt failed, loyal forces are still controlling all strategic points," army chief Niyongabo said in a statement also broadcast on state radio earlier in the day.

In Burundi's civil war that ended in 2005, the army was commanded by minority Tutsis who fought against rebel groups of the majority Hutus, including one led by Nkurunziza.

The military has since been reformed to absorb rival factions, but fault lines in its ranks have remained, fuelling fears of a slide back into ethnic bloodletting that have caused deep concern in Burundi's neighbors.