South African police arrested 19 suspected Congolese rebels, including two senior members of the M23 group, on suspicion of running an illegal military operation, law enforcement officials said on Tuesday.
M23 rebels have carved out a fiefdom in eastern Democratic Republic of Congo's North Kivu province, dragging the region back into war and displacing an estimated three quarters of a million people.
The group may have been training for a military attack on Congo's government, said a law enforcement source who asked not to be named. He said it included senior M23 members but a police spokesman would not comment on that.
The group was taken into custody in South Africa's northern Limpopo province after an investigation by a crime intelligence unit, police said.
"More arrests might be coming," police spokesman Lindela Mashigo said, adding the 19 were expected to appear in a Pretoria court this week to face a charge under South Africa's Foreign Military Assistance act.
Congo's government spokesman Lambert Mende said authorities had "known for a long time that there have been activities outside the country (to destabilise Congo)".
Mende did not know if those arrested were M23 members but added there were a "good number of people in South Africa" sympathetic to former leader Mobutu Sese Seko - veteran dictator of Congo, previously known as Zaire, who died in 1997 after being overthrown by the father of President Joseph Kabila.
The M23 rebels, who launched their offensive after accusing Kabila of reneging on the terms of a March 2009 peace agreement, have since broadened their goals to include ousting Kabila and "liberation" of the whole of Congo.
South Africa, the richest country on the continent, has for years attracted characters who have had to flee their homes for political reasons or to escape criminal charges.
In a high-profile case, a Johannesburg court in January found a suspected former Niger Delta rebel leader guilty of masterminding two deadly car bombings in Nigeria in 2010 while living in South Africa.
-reuters