Freetown - Twenty-four United Nations staff and others were killed when a helicopter crashed on Tuesday into a hillside in thick jungle in Sierra Leone, UN officials said.

The helicopter, leased by the UN peacekeeping mission in the West African country, crashed about five minutes away from its destination, the eastern town of Yengema, on a flight from the capital Freetown, UN officials said.

"All are presumed to have perished. It crashed into a hillside in a thick jungle area," said Sharon McPherson, an information officer with the UN mission.

Three Russian pilots were among the dead, a UN spokesperson said at the world body's headquarters in New York.

The helicopter was a Russian Mi-8 MTV-1 from the UTair company, which has been involved in UN peacekeeping operations from East Timor to Iraq. The company has been used by the United Nations since the collapse of the Soviet Union.

The United Nations has some 11 000 peacekeepers in the UN Mission in Sierra Leone, known as UNAMSIL.

McPherson said there was no immediate word on what had caused the crash.