The International Committee of the Red Cross (ICRC) has pulled 71 of its international staff out of Yemen because of rising security threats, Al Jazeera reported.
Some 450 ICRC employees remain in Yemen, including dozens of expatriate staff, spokeswoman Marie-Claire Feghali said.
The aid agency urged all sides in the country's three-year war to provide security guarantees so its staff could keep running surgical, water and food assistance programmes, which it said had been "crippled" by the partial evacuation.
"The ICRC is calling on all parties to the conflict to provide it with concrete, solid and actionable guarantees so that it can continue working in Yemen.
The agency said moving the majority of its staff Djibouti was due to high risks in the war-torn country.
An ICRC employee, a Lebanese national, was killed on April 21 by an unknown gunmen who opened fire on his car in the southwestern Yemeni city of Taiz as he was on his way to visit a prison, it said at the time.
"Our current activities have been blocked, threatened and directly targeted in recent weeks, and we see a vigorous attempt to instrumentalise our organisation as a pawn in the conflict," the ICRC said in a statement.
"While the Yemen delegation has received numerous threats in the past, we cannot now accept additional risk less than two months after a gunman killed a staff member. The security of our staff, who are being intimidated by parties to the conflict, is a non-negotiable prerequisite for our presence and work in Yemen and an absolute priority," the statement added.