An Ethiopian military cargo plane crash landed and burst into flames Friday at Mogadishu airport, killing four of its six crew members, Somali security officials at the site 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 belonged to the Ethiopian military.

The Ethiopian foreign affairs ministry in Addis Ababa was not immediately able to confirm if the crashed plane was Ethiopian.

Ethiopia sent troops into Somalia in 2011 to fight Shebab Islamist insurgents.

A thick tower of black smoke was seen rising 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 might have been carrying ammunition or other inflammable products.

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