The medical aid agency, Doctors without Borders, says at least 33 people are still missing, five days after a deadly US airstrike on its hospital in the northern Afghan city of Kunduz.
"We are continuing to try to contact the [missing] staff. We cannot speculate on their whereabouts," the charity said in a statement on Thursday.
The agency, known by its French acronym MSF, said it has set up a hotline in a bid to trace 24 staff and the nine patients who are still unaccounted for.
The statement has sparked fears that the death toll may significantly rise. The latest tally for last Saturday's attack by US fighter jets stands at 22 dead.
Meanwhile, Guilhem Molinie, MSF's Afghanistan representative, said during a press conference in Kabul on Thursday that more bodies could be found inside the hospital.
"We are still in shock," said Molinie, adding, "We lost many colleagues and at the moment it's clear that we don't want to take the risk for any of our staff. We don't control the hospital."
Molinie also noted MSF has not yet received any assurances that would give them the "confidence" to return to Kunduz.
MSF General Director Christopher Stokes has also said that the charity was reviewing the security conditions of "all its operations in Afghanistan."
Following the deadly incident, the MSF said in a statement that the aerial assault continued for more than half an hour after US and Afghan military officials in Kabul and Washington were first informed.
MSF President Joanne Liu also said, “This was not just an attack on our hospital; it was an attack on the Geneva Conventions. This cannot be tolerated.”
She also called for an independent and impartial investigation into the incident.
“We cannot rely on internal military investigation by the US, NATO and Afghan forces,” said Liu, adding that International Humanitarian Fact-Finding Commission (IHFFC) was “the only permanent body set up specifically to investigate violations on an international humanitarian law.”
In the face of mounting pressure from international aid groups, US President Barack Obama apologized to the MSF chief, admitting that the strike was a mistake.
Kunduz has been the scene of fierce battles between the Taliban and Afghan forces since the militant group captured the strategic city in a blitz on September 28. Afghan forces then managed to retake the city.