Dr Muhammad Abu Salmiya, who heads al Shifa hospital in Gaza City, has been detained along with "some of the medical staff", a spokesman said.

Hamas said it "strongly condemned" his arrest, describing it as "nothing less than despicable" and "lacking any sense of humanity and morals".

The group said it was a "flagrant violation of international norms and charters" given there are "obligations to ensure that medical personnel are never harmed, including in times of war".

Hamas is calling on international bodies including the Red Cross and World Health Organisation (WHO) to evacuate the remaining patients from al Shifa.

It is also asking them to secure Dr Salmiya's release, along with the medical personnel who were "arrested simply for continuing to fulfil their humanitarian duty", it said.

On Sunday, the WHO described al Shifa as a "death zone" after medical experts visited the besieged facility.

Only 291 patients remained, it said, alongside 25 health workers.

Dr Salmiya's arrest has not been confirmed by the Israel Defence Forces (IDF).

The development follows the discovery of what Israel claims is a 55-metre tunnel beneath the 20 acre complex, which it says Hamas has been using for military purposes.

At one end it contains a blast door with a firing whole, according to the IDF.

At another entrance troops found a bathroom, a kitchen and an air conditioned meeting room, the IDF added.

Hamas used the hospital as a "human shield", said Colonel Elad Tsuri, commander of an Israeli armoured brigade that discovered the tunnel.

Air conditioning means they were able to "stay for a long time", he added.

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The IDF claims to have uncovered and destroyed 400 Hamas tunnels inside Gaza since it launched its ground operations.

It claims many of the shafts leading to a tunnel network are "located within civilian hospitals, schools and homes".

Israel has long accused Hamas of using civilian infrastructure including hospitals as command centres - something the group denies.

Claims on the number of destroyed tunnels are unverified.