The UN has said 'there needs to be justice' following Israel's double strike on a Gaza hospital which killed at least 20 people, as an initial Israeli military probe said the strike targeted a 'camera positioned by Hamas'.

Condemnation of the attack, whose victims included five journalists and four health workers, has been mounting, with UK Prime Minister Keir Starmer describing it as 'completely indefensible'.

Later on Tuesday the Israel Defense Forces (IDF) released its initial inquiry, which identified several 'gaps' for further investigation.

It came as Israelis launched a day of nationwide protests calling on their government to accept a deal to release the hostages.

Monday's attack on Nasser hospital in Khan Younis saw an initial strike kill at least one person before a second in the same location about 10 minutes later hit journalists and rescuers who were attending the scene.

At least 20 people were killed including four health workers and five journalists who worked for international media outlets, including the Associated Press, Reuters, Al Jazeera and Middle East Eye.

'This is a shock and this unacceptable,' UN human rights office spokesperson Thameen al-Kheetan said on Tuesday. 'This raises many, many questions about the targeting of journalists and all of these incidents must absolutely be investigated and those responsible must be held accountable.'

In its statement, the IDF said it identified a camera positioned by Hamas in the area of the hospital 'used to observe the activity of IDF troops'. 'The troops operated to remove the threat by striking and dismantling the camera,' the statement said. It alleged that six of those killed were 'terrorists'.

In Israel, protests against the government have intensified, with demonstrators blocking highways to demand a ceasefire and an immediate resolution regarding hostages held by Hamas.

The situation in Gaza continues to deteriorate, with humanitarian crises escalating as many face starvation and displacement amidst ongoing conflict.