The medical charity MSF says at least three of its staff were killed in the Afghan city of Kunduz after a clinic was hit by an air strike on Saturday.
US forces were carrying out air strikes at the time. The Nato alliance has admitted the clinic may have been hit.
MSF says more than 30 staff are unaccounted for. The hospital had 105 patients at the time.
There has been intense fighting in Kunduz since Taliban fighters swept into the northern city on Monday.