South Africa's decision to contribute troops to the Southern African Development Community (SADC) Mission has been denounced by the main opposition as a mistake.

But the defence minister defended the deployment, labelling the claims of the Democratic Alliance (DA) "a blue lie" during a ceremony at an air force base on the outskirts of Pretoria where the bodies arrived.

"When membership of the national defence force are sent out to any mission... their preparedness is checked," defence minister Thandi Modise said.

Family members sat quietly as they watched the coffins of their loved ones, covered by the national flag, carried by South African Defence Force (SANDF) comrades.

Captain Simon Mkhulu Bobe and Lance Corporal Irven Thabang Semono were killed a week ago when a mortar landed inside one of the South African contingent's bases near the eastern city of Goma.

"We are taking each day as it comes, as difficult as it is, grieving," Bonga Bobe, the brother of one of the deceased told media on the sidelines of the ceremony, adding: "He had so much love".

Bobo also added his family was "still happy" with the support they were receiving from the government "so far".

Last week, the DA alleged the SANDF "does not have the capacity to effectively pursue an anti-insurgency campaign... neither does it have the prime mission equipment to support the ground forces".

The deaths mark the first fatalities for South Africa since it began deploying 2,900 soldiers in eastern DR Congo in mid-December.

They were sent as part of a southern Africa regional force alongside soldiers from Tanzania and Malawi, tasked with helping DRC government forces fight M23 rebels.

"We went because sometimes for the region to make peace we must allow one neighbour to make peace among themselves," Modisa said.

"Much as it's breaking our hearts to get the bodies back... it's also giving the South African troops" the "necessary experience".