A suicide bomber detonated explosives at the gate to Red Cross offices in the Afghan city of Jalalabad on Wednesday.
Following the blast two gunmen entered the building and began fighting with Afghan security forces.
Witnesses described thick smoke and heavy gunfire.
Six foreign Red Cross staff members were rescued by police and are safe, an Interior Ministry spokesman said.
The attack came less than a week after a band of insurgents assaulted the office of the International Organisation for Migration (IOM) in Kabul, killing three civilians and injuring four foreign aid workers.
The Red Cross operations in Afghanistan are the group’s biggest in the world. It has some 1,800 staff working on projects ranging from providing orthopedic limbs to the war wounded to visiting militants in Afghan jails.