Clashes between a militia and a self-defense group in southeastern Central African Republic have left at least 30 civilians dead including six Red Cross volunteers who were attending a crisis meeting at a health facility, officials said Wednesday.

The violence took place late last week in the town of Gambo, which is about 75 kilometers (47 miles) from Bangassou, a town that has been a flashpoint amid the upsurge of bloodshed in the long chaotic country.

"We are appalled by the news of the death of our fellow volunteers," said Antoine Mbao-Bogo, president of the Central African Red Cross. "We call on all parties to take steps to spare the civilian population, and to respect all humanitarian workers."

The deaths marked the third such attack on the Red Cross this year, officials said. Many humanitarian workers have been blocked from doing their work, and militants also have tried to kill wounded enemies in public health facilities.

Read more: ABC News