The Israeli military said it had "concrete intelligence" that Hamas operatives had regrouped there. Palestinians have told the BBC of their fears at being trapped in fierce battles.

While this week's raid again highlights a desperate humanitarian situation, it is also a strong reminder that Hamas is far from a spent force.

Some analysts suggest it shows the desperate need for a comprehensive strategy to deal with the Islamist armed group and a clear plan on the post-war governance of Gaza.

The Israel Defense Forces (IDF) now claim to have killed "over 140 terrorists" in ongoing fighting at al-Shifa and to have made some 600 arrests, including dozens of top Hamas commanders as well as some from Islamic Jihad. Two Israeli soldiers have also been killed.

Israeli reports suggest that in recent weeks the army found that senior Hamas figures had resumed operations at al-Shifa and that some even took their families to the hospital. The IDF says it uncovered arms caches and a large quantity of cash at the site.

Hamas has denied that its fighters were based there and claims that those killed were wounded patients and displaced people.

Palestinian witnesses have told the BBC that gunfire and Israeli air strikes have been endangering patients, medics and hundreds of people still sheltering in the grounds.

A local journalist has shared footage of smoke billowing from the complex.

In another unverified video, shared on social media, dozens of women can be seen hunkering down in a building with their children. One says: "They took our men to an unknown place and now they're asking women and children to leave. We don't know where we'll go".

In the background, an IDF officer says over loudspeaker: "Do not leave the buildings without instructions. We seek to evacuate civilians without harm, as we did in other hospitals in the past."

Since Wednesday evening, communications have been severely restricted, making it hard to contact medics and others at the scene.

Back in November, there were accusations of possible violations of international law as Israeli tanks closed in on al-Shifa, in the heart of Gaza City. Premature babies were among those who died as conditions deteriorated in the besieged hospital.

The IDF released surveillance camera footage which showed two hostages snatched from Israel being taken into the hospital. After an extensive search, Israeli troops blew up a large tunnel with rooms which ran under the site and later withdrew.

The Israeli army went on to suggest that Hamas's regional brigades and battalions in the north of the Gaza Strip had been disbanded. But soon reports emerged that small cells were regrouping.

While Hamas has undoubtedly been severely weakened by the war, there have since been signs that it has been trying to restore its governing capability, including through policing and with some possible involvement in aid distribution.

Washington has indicated that Israel's renewed military action at al-Shifa Hospital illustrates its worry that its close ally does not have an adequate strategy to dismantle the organisation.

"Israel cleared Shifa once. Hamas came back into Shifa, which raises questions about how to ensure a sustainable campaign against Hamas so that it cannot regenerate, cannot retake territory," the US National Security Adviser, Jake Sullivan, said this week.

The US has been pressing Israel to come up with a feasible alternative for Hamas rule in Gaza. Its plan has been to promote individuals linked to the internationally recognised Palestinian Authority (PA) and to work with Arab states to prevent a power vacuum.

Israel previously said it was seeking to cooperate with clan leaders in Gaza without affiliation to the PA or Hamas.

Now, the Wall Street Journal has reported that Israeli security officials are "quietly developing a plan to distribute aid", working with Palestinian leaders and businessmen not linked to Hamas. The suggestion is that this "could eventually create a Palestinian-led governing authority".

Israeli media have suggested the operation at Shifa Hospital could last for several days. It is not being linked to the military operation in Rafah which Israel insists it must carry out to win the war with Hamas.

There has been international concern over the impact such an offensive on the Egypt border could have as more than half of the 2.3m residents of Gaza are now displaced there.

"It's going to happen. And it will happen even if Israel is forced to fight alone," the Israeli Strategic Affairs Minister, Ron Dermer, told the Call Me Back with Dan Senor podcast.

While the IDF has formulated operational plans for Rafah and handed these to Israel's government, no order has yet been given to execute them.

It is seen as unlikely that such a move will take place during the Islamic holy month of Ramadan, which ends around 9 April. It would also take time for Israel to build up the necessary forces in Gaza.

Despite declarations to the contrary, Israeli experts also believe that in order for a Rafah operation to be effective, ultimately coordination will be needed with Egypt and the US.

"The Egyptians are on the other side of the border," pointed out retired General Amos Gilad on Israel's Kan Radio. "You can't do anything in Rafah without coordinating with the Egyptians and the Americans."

bbc