A South African working for a British oil company has been released unharmed after he was kidnapped in the volatile eastern Democratic Republic of Congo, the foreign department said Thursday.

"He has been released, he is now safe and unharmed," said spokesman Clayson Monyela, adding that the man was still in the DRC.

"The South African government worked very closely with the authorities in the DRC through our embassy as well as his employer to negotiate and secure his release."

The man, whose family asked that his name was not made public, was kidnapped Monday while travelling with Congolese soldiers in the Virunga National Park, a UNESCO World Heritage Site.

Monyela said he was released Wednesday around 5:00 pm, adding that the foreign department could not yet give details on how he was freed.

"I've been requested by the people that negotiated his release not to go into those details at this stage," he said.

The Congolese army accused Hutu rebels from neighbouring Rwanda of carrying out the kidnapping.

A spokesman for oil and gas company SOCO Exploration and Production DRC, a subsidiary of London-based SOCO International, said the man had been on a mission to secure the volatile area in Nord-Kivu province, where Hutu rebels have long operated.

The company in June 2010 clinched a contract to explore for oil reserves there.

Another South African who was also taken hostage during the kidnapping in the Katiguru area, north of the provincial capital Goma, had already been released, the army said.

Several armed groups have been active in Nord-Kivu province since the 1990s and they are regularly accused of violence against the civilian population, including rape and looting.

Democratic Force for the Liberation of Rwanda (FDLR) rebels have been operating out of eastern DR Congo since the aftermath of Rwanda's 1994 genocide. Some of its members are accused of being among the main perpetrators of the massacres of Tutsi minorities.