Armed men on horseback killed a worker with Medecins Sans Frontieres (MSF) in Chad’s embattled southeast and wounded another, while seven employees of the relief agency and 3,200 displaced people they were assisting remain missing, MSF said on Monday.

The attack occurred on Wednesday and Thursday around the town of Koloy where some 5,000 displaced people had gathered in the past month, said Mercedes Tatay, MSF's emergency manager.

"Some armed men entered the village and burned several market stands," Tatay told IRIN by phone from Paris. "There was a clash with some self-defense militia within town, there was looting all through the houses within Koloy and three other villages. And the population was threatened not to go back to Koloy and therefore fled the area."

"The MSF clinic and all the water supply materials we had in Koloy itself were looted or broken or stolen, as were drugs,” she said.

Koloy is about 100 km northeast of the relief hub of Goz Beida.

Initially, MSF reported that 37 members of its staff and 5,000 displaced people were missing. Tatay said 30 MSF workers have been accounted for while seven others were missing.

"We’ve confirmed the death of one of our workers who died during the attack and in Goz Beida we’ve received another who had been wounded," she said.

About 1,800 displaced people were gathering around the town of Ade, Tatay said, citing information gathered from the International Committee of the Red Cross (ICRC), which had gone to the area. MSF was preparing to go to Ade, about 35 km northwest of Koloy, on Tuesday. Some 3,200 displaced who were in Koloy remained unaccounted for.

"Either they’re still on the move or they’re still arriving in and around the Ade area, which we’ve heard from some of them is where they feel safer at this stage," Tatay said.

The United Nations refugee agency (UNHCR) and other aid agencies in Chad have been asking for increased protection since last year when a spate of hijackings and attacks on aid workers started. Some areas of eastern Chad have become too dangerous to visit, and most UN convoys travel with a heavily armed Chadian military escort.

Relief workers say violence has escalated in southeastern Chad in the past month with inter-communal clashes claiming more than 200 lives. Analysts say the nearly four-year old conflict in neighbouring Darfur region of Sudan has made weapons easily available and that as Chad’s government diverts its military to crush an internal rebellion the eastern border area has been left vulnerable.

Some 68,000 people have been displaced in eastern Chad. The Chadian government on Monday declared a state of emergency in the region to counter the worsening violence.

“What is obvious is that for the whole year there has been Chadian population at the border who have been under threat and displaced at multiple locations and trying to move toward safer areas that eventually happen not to be that safe,” Tatay said. “There is continuous displacement that renders this population extremely vulnerable.”