By Mark Dummett BBC, Mbuji Mayi

Zimbabwean troops defending Democratic Republic of Congo's diamond capital, Mbuji Mayi, are due to return home on Friday.

A ceremony was held at the airport in the town to mark the imminent departure of the soldiers, which was delayed by a shortage of aircraft.

. This is part of the withdrawal of the Zimbabwean forces from DR Congo, where they have been supporting the Kinshasa government for the last four years.

Zimbabwe sent an estimated 12,000 men to fight alongside the Congolese army in its four year struggle against rebels and their Rwandan and Ugandan backers.

Following recent agreements between the DR Congo Government and both Rwanda and Uganda, Zimbabwe decided that it could withdraw its troops without threatening the government's security.

Since mid-August, Zimbabwe says it has already pulled men out of other key towns and that all the rest will follow soon.

Held the diamonds

The Zimbabwean army has been the Congolese Government's most loyal and important ally.

It was near here four years ago in the diamond fields surrounding Mbuji Mayi that it showed just how important it was.

Without much help from their disorganised Congolese allies, the Zimbabweans stopped and then held back the rapid advance of the rebel and Rwandan armies which were then threatening to march unhindered all the way across Congo.

Mbuji Mayi was the prize - the Congo's diamond capital and the government's biggest source of export earnings.

Zimbabwe committed large forces to DR Congo

If it had fallen, the fear was the government would have collapsed, too.

Troops out

Zimbabwe made sure this did not happen, but since then has been accused of profiting from its role in the war, not least from the lucrative industrial diamond mines in this part of the country.

The first contingent of Zimbabwean army soldiers is due to leave on Friday.

Troops have already left several other key towns in recent weeks, with the rest - which Zimbabwe numbers at 3,000 - to follow soon.

Zimbabwe says it can do this since Congo signed a peace deal with Rwanda at the end of July which should lead to the withdrawal of all Rwandan soldiers from Congo as well.