A Ugandan military helicopter with eight people on board crashed and caught fire at the main international airport in Somalia's capital, Mogadishu, a Ugandan army spokesman has told the BBC.

Three people escaped with burns but the other five were "yet to be accounted for" following the crash at the Aden Adde International Airport, Maj Gen Felix Kulaigye said, adding that its cause was still unclear.

"We heard the blast and saw smoke and flames over a helicopter. The smoke entirely covered the helicopter," Farah Abdulle, one of the airport staff, told Reuters news agency.

Somalia's state-run news agency reported that the fire was quickly contained by the emergency services.

Ugandan troops are part of an 11,000-strong African Union (AU) force helping the government fight the al-Qaeda-linked al-Shabab group, which has been waging a brutal insurgency in Somalia for more than two decades.

The head of the Somali Civil Aviation Authority, Ahmed Maalim, told the BBC that the helicopter had come down in the airport's military section after flying in from the Balidogle airbase in the Lower Shabelle region, about 90km (56 miles) north-west of Mogadishu.

In a statement, the AU mission in Somalia said the three survivors had been taken to hospital for treatment, while operations were under way to "retrieve the remaining crew and passengers.

Both AU and Somali officials said an investigation was under way to establish the cause of the crash.

It delayed the departure of a Turkish Airlines passenger plane, but domestic flights have continued to operate normally. (BBC)