Congolese rebels seek foreign investors to tap fabulous mineral wealth buried under one of the world's most volatile patches of Congolese real estate.

Diamonds, gold, and other riches are all there for the taking, says Congo's RCD rebel movement, if only mining companies would shake off a misplaced fear of stepping into Africa's biggest war.

"It's a geological scandal," Nestor Kiyimbi Mutangi, the RCD's minister for mines, land and energy, told Reuters in a weekend interview.

"There's such a variety of minerals and in such large quantities," he said in the eastern Congolese city of Goma.

Four years of war has left only one industrial-scale mine operational in RCD territory, but the rebels say there are fantastic concessions available, not to mention tax breaks, for willing partners.

Many investors have so far proved reluctant to commit capital to anarchic eastern Congo, where the war has killed an estimated two-million people and a bewildering array of armed groups rape, loot and murder with impunity.

Rwandan troops, who invaded Congo in 1998 to back the RCD's campaign to topple the government, began withdrawing from Congo this month under a peace deal, stoking fears of worse instability as the war's most powerful force retired.

But the RCD, the biggest of several rebel movements in the former Zaire, says it will guarantee security for any firm willing to pay $50 000 for a 20-year mining concession.

"We offer foreign investors security and the guarantee of repatriating profits," Mutangi said. "They say we're rebels, but it's a modern rebellion, organised like a state".

Critics say the RCD, left out of a power-sharing deal between the Kinshasa government and several other rebel factions in April, has never had much popular support and has faced armed rebellion by dissidents who regard it Rwanda's stooge.

Intrepid investors may have to overcome other scruples.

United Nations experts have accused Rwanda and other belligerents of massive looting of Congo's minerals, but Mutangi said the charges against Rwanda were biased.

"There's no looting," he said. "You can't operate in the mining sector unless you follow the rules".

The RCD also denies multiple allegations of human rights abuses. In one of the latest accusations, UN investigators said RCD forces massacred more than 150 people in the diamond city of Kisangani in May.

Decapitated bodies were pulled from a nearby river in bags or with stones crammed in their slit stomachs to make them sink.

But, clutching a tin ingot paperweight bearing the name of a firm from the former colonial power Belgium, Mutangi said the RCD was in talks with various foreign companies.

"Others are waiting for the end of the war before they come back," he said.

Potential investors could look to the sole industrial mine operating in RCD territory – the Somikivu firm, extracting nobium oxide in Lueshwe, 160 km (100 miles) north of Goma.

Nobium oxide, mainly produced in Brazil and Canada, is used to make heat resistant alloys used in devices like rocket parts and to manufacture electronic superconductors.

Producing a plastic phial of the beige-coloured powder, which has an acrid, musty smell, Mutangi said the mine produced 270t of semi-processed nobium a month, purchased by Somikivu's German parent GFE for $675 000.

Nobium – named after a figure from Greek mythology who was punished for boasting about her 14 daughters – is only one of a treasure trove of minerals in the third of the Democratic Republic of Congo nominally held by the RCD.

Coltan, used for components in mobile phones and stealth bombers, as well as related minerals like tin ore and wolframite are all available, as are semi-precious stones like amethyst and tourmaline.

Most minerals are dug up by impoverished villagers toiling in the soil with spades, but for industrial miners, the RCD says the rewards outweigh risks.

"There are big concessions for whoever wants to come here," Mutangi said. "Every one dollar invested here produces four dollars in your country."