CAPE TOWN, South Africa (AP) — Congo ’s government is questioning Apple about the tech company’s knowledge of “blood minerals” from a conflict zone in the African country that could be smuggled into its supply chains and is demanding answers within three weeks.

A group of international lawyers representing Congo said Thursday that they sent letters to Apple’s CEO Tim Cook and its French subsidiary this week, raising concerns about human rights violations involving the minerals extracted from mines in the country’s troubled east that might end up being used in the company’s products. They included a list of questions challenging Apple to show how it monitors its supply chains in a region where more than 100 armed rebel groups operate, some of whom have been accused of carrying out mass killings of civilians.

Writing to Cook, the lawyers said “it has become clear to us that year after year, Apple has sold technology made with minerals sourced from a region whose population is being devastated by grave violations of human rights.”