Four suspects named in an application made at the opening of an inquest into the murder of Rwandan dissident Patrick Karegeya in South Africa, could further strain relations between the two countries.

The four — Appollo Ismael Kiririsi, Samuel Niyoyita, Nshizirungu Vianney and Alex Sugira — are Rwandan nationals.

The application on Wednesday was made by a lawyer representing the Karegeya family, Gerrie Nel, and was recorded as evidence by the magistrate at the Sandburg Court in Johannesburg.

Mr Nel told the magistrate that there had been no indication that "any" steps had been made to trace the suspects, and that there was "no contact with Interpol or any other international law enforcement agency.”

"This incident happened in 2013. We are now in 2019 and yet nothing has happened in as far as the suspects in this matter are concerned," said Mr Nel.

"There has been no extradition treaty; there has not even been a mutual legal system request to bring the suspects, who are well known to everyone, including the police, to book."

The inquest is expected to last 16 days and involve up to 30 witness testimonies.

It is not yet clear whether a criminal prosecution will follow, for which the suspects may be summoned for trial.

The magistrate, Jeremiah Matopa, adjourned proceedings and announced that a ruling on the application will be made on January 21.

Mr Karegeya’s widow, Leah Karegeya, flew to South Africa to attend the inquest from the US, where she lives in exile.

The late Karegeya, who lived in exile in South Africa, was strangled to death in a Johannesburg hotel in December 2013. No suspects were arrested or charged but relations between South Africa and Rwanda have soured since then.

In the aftermath of his murder, South Africa withdrew its visa regime for ordinary Rwandans and expelled three top diplomats in March 2014.

Rwanda responded by expelling six high-ranking South African diplomats.

A recent United Nations report implicates an opposition group that Mr Karegeya co-founded — Rwanda National Congress — in subversive rebel activities in the East African region. The UN report notes that RNC is recruiting fighters across the region for its rebel outfit group called P5, which is said to enjoy support from countries in the region, including Rwanda's neighbours.

Rwanda said that the activities of RNC put in question South Africa’s willingness and ability to prevent dissidents on its soil from engaging in political or armed activity.

Kigali also accused the South African Department of International Relations and Co-operation of choosing to believe "rumours against Rwanda over the assurances the country made.

"These include unfounded allegations made against Rwanda in public statements and the media, based on rumours and distortions propagated by Rwandan detractors based in Canada and South Africa, and media platforms associated with them,” a statement by Rwanda notes.