Aid officials say six Red Cross volunteers have been killed in Central African Republic, the third deadly attack on the group in the country this year.

Antoine Mbao-Bogo, president of the Central African Red Cross, said Wednesday he was "appalled" by news of the killings in the southeast.

The circumstances of the attack were not clear, according to the International Red Cross and Red Crescent Movement.

The Red Cross says the volunteers were in Mbomou prefecture attending a crisis meeting at a health facility.

Many humanitarian workers have been blocked from doing their work during the latest surge in largely sectarian violence in Central African Republic. Militants also have tried to kill wounded enemies in public health facilities.