The International Committee of the Red Cross (ICRC) has called for the immediate release of two staff members abducted during an ambush in northern Afghanistan last week that killed six workers.
The aid workers were in a convoy carrying supplies to areas hit by avalanches when they were attacked in the northern province of Jowzjan on February 8.
"We call on the abductors' sense of humanity and request the immediate, safe and unconditional release of our colleagues and to avoid taking any action that could endanger their lives," Monica Zanarelli, ICRC chief in Afghanistan, said in a statement released on February 18.
"We do not want the agony and heartache of this tragedy to deepen," she added.
No group claimed responsibility for the attack, but provincial Governor Mawlawi Lutfullah Azizi said he suspected Islamic State (IS) gunmen were behind it.
IS militants have made limited inroads in Afghanistan, but have carried out increasingly deadly attacks.
The killings come after a Spanish worker of the ICRC was abducted in northern Afghanistan in December and released less than a month later.
Neither the ICRC or Afghan officials said how he was freed or who was behind the abduction.
After the attack, the ICRC, which has been working in Afghanistan for three decades, said it was putting its nationwide operations on hold, although it added there were no plans to withdraw staff.