The World Health Organization voiced concern on Friday about the fate of the head of Gaza City's Al-Shifa hospital, whom Israeli forces detained over the facility's alleged use by Hamas.

The WHO said in a statement that the chief of the biggest hospital in the besieged Palestinian territory had been arrested on Wednesday along with five other health workers, while they were taking part in a UN mission to evacuate patients.

"Three medical personnel from the Palestine Red Crescent Society and three from the Ministry of Health were detained," the WHO said.

Since then two of the six have reportedly been released, but "we do not have information about the well-being of the four remaining health staff, including the director of Al-Shifa hospital," the statement added.

The UN agency called for "their legal and human rights to be fully observed during their detention".

A spokesperson for the Israeli army said on Saturday that hospital director Mohammad Abu Salmiya was being questioned.

"We are currently moving forward with… questioning him over the fact that he was the head of a hospital that was really sitting on top of an entire terror network," Doron Spielman said.

"How could he not know what's happening? We have hostages that were on, you know, CCTV in his hospital."

Abu Salmiya has been frequently quoted by international media about the conditions inside Al-Shifa, a major focus of the Israeli ground offensive following attacks by Hamas militants on October 7.

The Israeli army, which raided the hospital last week, has alleged that Hamas fighters used a tunnel complex beneath the facility in Gaza City to stage attacks.

Hamas and hospital officials have repeatedly denied the claims.

The WHO has carried out three missions to Al-Shifa in the space of a week, the organisation has said, on one occasion managing to evacuate 31 babies from the hospital.

During the third mission on Wednesday, which was carried out in cooperation with the Palestine Red Crescent, 151 people were evacuated, including patients, their relatives and healthcare workers, according to the WHO.