Passengers aboard a Russian-made Ilyushin 76 were sucked out when the cargo plane's back ramp opened as it flew high above the Democratic Republic of Congo, military and aviation officials said on Friday.

A Russian aviation official said he believed there were 129 passengers, a mixture of military officials and civilians, on the aircraft when the disaster occurred on Thursday evening during a flight from Kinshasa to Lubumbashi in the southeast.

But a government statement read out later on state television said there had been no casualties.

It was not clear how many people were in the plane, which returned to the capital after the incident.

Congo's Minister for Peace, Vital Kamerhe, confirmed the incident, but did not give details.

The government said the army would take journalists to Kinshasa airport to see the plane, chartered by the Congolese army.

Officials said it was common for the army and the government to charter cargo planes to transport military personnel and civil servants, often with their families, between Kinshasa and Lubumbashi -- Congo's second biggest city and home to a big military base.

The ruined state of Congo's road network means that long-distance journeys have to be made by air, though many aircraft are old and poorly maintained.

The four-engined Ilyushin 76 is widely used in Africa, West Asia, India and China.

It entered service in the 1970s as a heavy lifter with the Soviet armed forces and a freighter with the Soviet airline Aeroflot and proved an invaluable workhorse in both roles.

In the 1980s it flew numerous air supply missions into Soviet bases at Kabul and Bagram during the invasion and occupation of Afghanistan, hauling armour, troops and supplies. More recently it has seen action in Chechnya.

But concern about its safety has mounted in recent years because of the age of the aircraft and because they are often poorly maintained.

In February an Ilyushin 76 crashed in the mountains of southeast Iran, killing 276 elite Revolutionary Guards and crew.