Two Red Cross workers were fatally shot by an unknown assailant in northern Yemen on Wednesday, the organization announced.

The employees were a field officer and a driver, both Yemeni nationals, who were traveling from the northern province of Saada and killed in the province of Amran, Reuters reports. “Two of our colleagues were shot and killed in their car … as they were traveling back Saada to Sanaa,” Red Cross spokesperson Adnan Hizam said.

The organization believes there was only one gunman involved in the shooting but says the motivation was unclear.

“The ICRC [International Committee of the Red Cross] condemns in the strongest possible terms what appears to have been the deliberate targeting of our staff,” said Antoine Grand, head of the ICRC’s Yemen delegation.

A civil war in Yemen that began in March has caused a humanitarian crisis in the Arabian Peninsula nation as fighting has disrupted airports and seaports.

Time