GENEVA (AP) — A Swiss nonprofit campaigning group is calling on the country's federal prosecutor's office to open a criminal investigation into one of the world's largest processors of precious metals.

The organization, TRIAL, told a news conference Monday it filed a "criminal denunciation" against Swiss refinery Argor-Heraeus, based on evidence collected by a former U.N. investigator.

TRIAL director Philip Grant says the documents show the company may have refined three tons of gold ore obtained by armed groups in the Democratic Republic of the Congo through pillaging, a war crime. Kathi Lynn Austin, the former investigator, says that by refining the gold, the company essentially laundered it.

Argor-Heraeus said in a statement it "firmly refuses any such accusation" and was surprised by it because the U.N. already dealt with previous such claims.