Lubumbashi - Fifteen people have suffocated to death while digging in an illegal mine in south-eastern Democratic Republic of Congo, where the problem of illicit mining is widespread, an official said on Saturday.The incident occurred on Friday in Kolwezi in the mineral-rich province of Katanga, where scores of impoverished illegal miners risk their lives in search of minerals including copper and cobalt."Fifteen artisanal miners died yesterday in a tunnel in Kolwezi," Mayor Deoda Kapenda told AFP."The miners died by suffocation in a tunnel more than 20m deep. It was not a landslide."The victims also bore burn marks of unclear origin, he said.Despite its enormous natural resources, the Democratic Republic of Congo remains one of the world's least developed countries.