Burundi President Pierre Nkurunziza's attempt to return home amid reports of a coup has failed and he has returned to Tanzania where he was attending a summit, officials there told the BBC.

The coup was announced by Maj Gen Godefroid Niyombare on Wednesday.

But its outcome remains unclear and the presidency insisted it had failed.

Heavy gunfire was heard early on Thursday morning near the radio and TV station in the capital, Bujumbura, Reuters news agency reports.

There has been mounting unrest in Burundi since President Nkurunziza, who came to power in 2005, announced he was seeking a third term in office - apparently in contravention of the constitution.

The loyalists still reportedly hold the presidential palace and main radio offices.

"The attempted coup by General Godefroid Niyombare has been stopped," said armed forces chief General Prime Niyongabo said in a radio broadcast.

Earlier Gen Niyombare had ordered the closure of the airport to prevent Mr Nkurunziza's plane from landing.

The UN and US urged all sides to show restraint.

In his earlier announcement of the coup, Gen Niyombare said he did not recognise the leadership because the president's bid for a third term violated the constitution.

Gen Niyombare said in a radio broadcast: "The masses vigorously and tenaciously reject President Nkurunziza's third-term mandate. President Pierre Nkurunziza has been relieved of his duties. The government is overthrown."

A few hours later the Burundi presidency dismissed the coup attempt, saying: "It is with regret that we have learned that a group from the armed forces mutinied this morning and declared an imaginary coup.

"This coup attempt has been foiled and that these people, who read the coup announcement on the radio, are being hunted by defence and security forces so that they can be brought to justice."

Mr Nkurunziza had been in Dar es Salaam to discuss the crisis with regional leaders.

Tanzanian President Jakaya Kikwete said the summit had condemned the coup, adding: "The region will not accept, nor will the region stand by, if violence does not stop or escalates in Burundi."