This photo taken on April 28, 2004 shows a chain of volcanoes bordering the Virunga National Park in the Democratic Republic of Congo

A British energy company made illicit payments and exploited civil violence in a bid to gain access to oil resources in the Democratic Republic of Congo's Virunga National Park, an international NGO said Thursday.

London-based Soco International benefited from fear and violence during fighting by government and rebel forces as it sought access to Africa's oldest national park, according to the group Global Witness.

In a report, the non-profit called on the giant to withdraw from the reserve, home to 3,000 species, including the endangered mountain gorillas immortalised in the film "Gorillas in the Mist".

The report contains research collected by Global Witness during the making of a documentary film, "Virunga", which is to be released in November by Netflix.

The group said the film contains a recording of a Congolese intelligence officer closely allied to the oil company offering a park ranger thousands of dollars to spy on the park's chief warden, Emmanuel de Merode.

De Merode was shot in the stomach and chest by gunmen in April, shortly after handing in a report on Soco's activities to the regional public prosecutor. No one has been charged in the shooting.

Soco, which has condemned the attack, said any suggestion of its involvement was "completely unfounded".

Another recording appears to show a senior Soco official and one of the company's contractors admitting that the company made payments to rebels, the NGO said.

Villagers from Gisigari and Rugari in the Virunga National Park, north of Goma, gather on June 17, 2014

Soco has denied all the accusations in the report, and told AFP on Thursday that it "no longer has an operational presence in the DRC".

Despite its own environmental rules and international accords, the government of the conflict-wracked but resource-rich DRC awarded oil concessions in much of the park in 2007.

Global Witness said the British oil company had to account for its actions, and called on its shareholders—which include Church of England—to pressure for an independent investigation.

"This inquiry should look at allegations of corruption, secretive payments and the arrest and intimidation of opponents by Congolese security forces who support Soco," Global Witness said in a press release.

"We are also calling for authorities in the UK and the US to launch investigations into corruption allegations surrounding the company."

UNESCO has said oil exploration and exploitation would breach Virunga's World Heritage site status.

In May last year, another oil giant, France's Total—Soco's fellow concession holder—said it would not drill in Virunga National Park.

In June, it reached a deal with environmental campaigners from the World Wildlife Fund (WWF) promising to halt its hunt for oil in the park.