The Seleka rebel coalition seized control of Bangui last week and suspended the country's constitution. CAR President Francois Bozize fled the country and a CAR rebel leader has declared himself president.
Georgios Georgantas, the head of the CAR delegation for the International Committee of the Red Cross, said there's no electric power in the capital and water supplies are in jeopardy.
"The humanitarian situation in Bangui remains worrying," he said in a statement. "The buildings used to store food or supplies and many ICRC residences, have been completely or partially looted."
Seleka rebels reached a truce with the government in January. The U.S. State Department called on the coalition to respect the agreement but suggested both sides at to blame for the security breakdown.
Georgantas said all sides to the conflict need to respect international humanitarian law.
"The looting and ransacking of medical and humanitarian facilities must cease, so that aid can be brought unimpeded to people hard hit by the violence of recent days," he said.