The M23 armed group on Thursday denied accusations that its fighters had looted at least 500 kilograms of bullion from Twangiza Mining's gold concession in eastern Democratic Republic of Congo

The firm operating in South Kivu province, much of which is under M23's control, said this week that M23 had "secretly transported (the gold) through underground channels."

It also accused the rebels of using Rwandan technicians to extract geological data to resume and expand mining.

Rwanda has consistently denied backing M23 rebels, despite repeated allegations from U.N. experts and Western and regional governments.

At a press conference on Thursday, Corneille Nangaa, leader of a rebel alliance that includes M23, said the mine was not in operation and that only artisanal miners were working there.

He said M23 did not have the necessary equipment to operate a mine.

Nangaa has also accused Congolese government forces of attacking the site including with aerial bombing. He said civilians had been killed in those attacks but did not provide a death toll.

A drone strike on October 15 destroyed power generation infrastructure at the mine, the company said. It is not clear who was responsible for the drone strike.

Congo's government did not respond to a request for comment on the allegation.

M23 staged a lightning offensive this year that allowed them to seize more territory in eastern Congo than ever before. The group seized the mine in May.

Twangiza said it had lost over 100 kg of gold a month since the takeover, in addition to $5 million worth of equipment and materials.

The company is preparing to file a formal complaint with international arbitration and Congolese authorities, and has declared force majeure.

Armed groups have seized several mining sites in mineral-rich eastern Congo, according to U.N. investigators.

A U.N. Security Council briefing last year said M23 rebels were earning around $300,000 monthly from mineral taxes in the coltan-rich Rubaya region.