South Africa's opposition said Monday it plans to lodge a parliamentary motion to force the government to immediately withdraw troops stationed in the Central African Republic after 13 soldiers died there in a coup.

The deaths of the troops in battles with rebels who seized Bangui on March 24, South Africa's heaviest military loss since apartheid, has raised questions over why they were deployed in the volatile nation.

The official line has been that a small contingent was sent to train local forces under a 2007 deal between President Jacob Zuma and the now deposed Central African president Francois Bozize.

But local media reports suggested that the soldiers were sent to protect the business interests of certain South African politicians in the Central African Republic.

The opposition Democratic Alliance said in a statement it would submit an urgent parliamentary resolution "to compel the president to bring our soldiers back home".

"Given the continued controversy surrounding the deployment, the lack of a clear mandate for our troops to remain in the CAR, the continued risk to the soldiers' safety and rumours that the (military) is considering a 'revenge' mission into the CAR, we believe the entire... presence should be withdrawn immediately," it said.

Zuma is under pressure to explain why troops were sent to the Central African Republic and to give details on what happened during the deadly battle for Bangui.

"The conclusion is inescapable that the South African troops were deployed to defend the faltering and dictatorial Bozize regime," the Democratic Alliance said.

The party wants parliament, which is on recess, to reconvene to discuss the issue.

Around 200 South African troops fought some 3,000 rebels from the Seleka coalition which seized control of Bangui and has now set up a government with several opposition figures headed by new strongman Michel Djotodia.

Zuma is due Wednesday to attend an extraordinary summit of the Economic Community of Central African States (ECCAS) in Chad.

The ruling African National Congress has in the meantime defended the troop deployment as in line with South Africa's foreign policy and that it was endorsed by the United Nations and the African Union.

In a statement Monday, the ANC denied allegations in the weekly Mail & Guardian that a company linked to the party had business operations in the Central African Republic which could have been one of those protected by the troops.

By making such accusations, the ANC said the paper is "pissing on the graves of gallant fighters who put their lives on the line in service of our country and our continent."