An Ethiopian military cargo plane crash landed and burst into flames Friday at Mogadishu airport, killing four crew members, officials with Somali security and AU forces said.

"It was a military cargo plane and there were six crew on board," said one security official who asked not to be named.

"Four of them died and two were rescued," the official said.

He said the aircraft, which crashed shortly before 0500 GMT belonged to the Ethiopian military.

A thick tower of smoke was seen billowing up from the crash scene and the airport was closed.

Sources at the airport said a series of explosions was heard as the fire spread along the plane, suggesting it was carrying ammunition or other inflammable products.

The African Union force in Somalia (Amisom) confirmed on its Twitter feed that the wrecked aircraft belonged to the Ethiopian airforce, expressing "heartfelt condolences to the government and people of Ethiopia following the loss of crew members."

The Ethiopian foreign affairs ministry in Addis Ababa was not immediately able to comment.

Ethiopia sent troops into south-west Somalia in 2011 to fight Shebab Islamist insurgents, alongside the Amisom force.

The Ethiopian troops have been crucial in dislodging the Shebab from a series of key towns.

Nick Kay, the UN special representative to Somalia, tweeted that he offered his "condolences" for the "tragic crash".