Proper procedures were followed in the expulsion of Rwandan diplomats from Pretoria, International Relations Minister Maite Nkoana-Mashabane said on Tuesday.

"We are guided by internal and also by international laws that govern such relations. We follow the same rules in the relation between South Africa and Rwanda," she said in Pretoria.

"Whatever action South Africa took in the past few days, we were unemotional. We had informed the Rwandese government in accordance with the norms that apply and informed by our Constitution."

Earlier this month, South Africa expelled three Rwandan diplomats, one of whom has reportedly been linked to an "attempted hit" on exiled Rwandan army chief Faustin Nyamwasa at his home in Johannesburg.

A few days later, Rwanda responded by expelling six diplomats based at the South African mission in its capital Kigali.

While Rwandan Foreign Minister Louise Mushikiwabo said at the time that the expulsions were "in reciprocity", there is speculation that the decision to exactly double the number expelled is a signal Rwanda is prepared to up the ante.

Nyamwasa, who is a former rival and critic of Rwandan President Paul Kagame, survived an assassination attempt in Johannesburg in 2010.

He and his family were not at home when the latest attack happened, reportedly having been moved to a safe place.

Nyamwasa and former Rwandan spy chief Patrick Karegeya were founding members of the opposition Rwanda National Congress. Karegeya was murdered in a Johannesburg hotel room on New Year's Eve.

Other Rwandan exiles have accused Kagame and his government of being behind Karegeya's death and the latest attack on Nyamwasa.

Kagame and other senior Rwandan officials have denied any involvement in the attacks.

Also last week, South Africa expelled a Burundian diplomat - Jean-Claude Sindayigaya, the first secretary of the embassy of Burundi - but has offered no reasons for sending him home.