Kinshasa - Doctors Without Borders says it is worried that intense fighting between the military and armed groups in eastern Democratic Republic of Congo could endanger its staff taken hostage there.
In a statement on Tuesday, the aid group said four Congolese team members were kidnapped during a July rebel attack in Kamango.
The charity said it has not had any contact with them since and is increasingly concerned for their safety.
Eastern DRC has long been plagued by myriad armed groups vying for control of the mineral-rich region.
Meanwhile, the UN Special Representative Mary Robinson visited another violence-plagued area of the country's east on Tuesday. She called for members of the M23 rebels who had committed crimes against humanity to be brought to justice, noting that they should not benefit from a government amnesty.