Israel struck Nasser Hospital at least four times during its deadly attack in southern Gaza on Monday, an analysis of new video footage by BBC Verify has found.

The attack, which has attracted international condemnation and widespread anger, reportedly killed at least 20 people, including five journalists.

Initial reports from Gaza said that Israel had struck the hospital twice, with the first blast followed nine minutes later by another which hit first responders and journalists who arrived at the scene.

But new analysis suggests the hospital was struck four times in total. BBC Verify and expert analysis found that two staircases were hit almost simultaneously in the first wave, and while what was thought to be a single later attack was in fact two separate strikes hitting the same place within a fraction of a second.

Israel does not allow international journalists to enter Gaza independently. BBC Verify identified the additional strikes by analysing dozens of videos provided by a freelancer on the ground and material filmed by eyewitnesses that circulated online.

In the first incident, an Israeli strike hit the exterior staircase on the hospital’s eastern side at 10:08 local time (07:08 GMT), killing journalist Hussam Al-Masri who was operating a live TV feed for Reuters.

BBC Verify has now identified another previously unreported blast at a northern wing staircase at practically the same time, which was overshadowed by the “double-tap” strike on the eastern staircase.

New footage shows smoke rising and damage at both staircases, while emergency workers said the hospital’s operating department was hit.

Other videos show an injured person being carried down the northern staircase and the hospital’s nursing director holding shredded and bloodied clothing which he said was being worn by a nurse while she was working in the operating department when it was hit.

N R Jenzen-Jones – the director of Armament Research Services, an arms and munitions intelligence company – said the footage “appears to show interior damage consistent with a relatively small munition, including an entry hole that suggests a munition with a relatively flat trajectory”.

Roughly nine minutes later, while dozens of first responders and journalists gathered on the eastern staircase, Israeli forces struck the facility again.

While the blast was documented by media at the time, frame-by-frame analysis of newly emerged footage clearly shows that two separate projectiles fired by Israeli forces hit the hospital milliseconds apart at an exposed stairwell where journalists and emergency workers had gathered.

Experts disagreed on the type of munition used in the third and fourth strikes.

Some munitions analysts with whom BBC Verify shared footage with identified the projectiles as Lahat missiles, a guided munition which can be fired from tanks, drones and helicopters. Several outlets in Israel have suggested that the munitions used against the hospital were fired by Israeli tanks stationed nearby.

The experts who spoke to BBC Verify said the blasts could not have been caused by a single tank, due to the quick succession in which the munitions hit the hospital.

“If these Lahats were fired from the ground, then at least two tanks would have been involved, as the interval between the two impacts is far too short,” Amael Kotlarski, an analyst with the Janes defence intelligence company, said. “No tank loader could have reloaded that fast.”

Meanwhile, Mr Jenzen-Jones said that the “impact of two projectiles at nearly the exact same moment suggests two tanks may have fired on the target simultaneously”.

Although he said it wasn’t possible to definitively identify the munitions used, the apparent physical characteristics and pattern of flight “suggest a ‘multi-purpose’ tank gun projectile, such as the Israeli M339 model”.

Satellite images reviewed by BBC Verify show IDF forces 2.5km north-east of Nasser Hospital and within firing range on the day of the attack. Other armoured vehicles can also be seen nearby.

The Israel Defense Forces (IDF) said it had no additional comment on the newly identified blasts when approached by BBC Verify.

Israel’s narrative of the attack has evolved since Monday’s attack. It initially said it had carried out a strike in the area of the hospital, saying that it “regrets any harm to uninvolved individuals ” and that an initial inquiry would be opened as soon as possible, but provided no justification for the attack.

In the hours that followed Prime Minister Benjamin Netanyahu said Israel was responsible and that it “deeply regrets the tragic mishap”.

On Tuesday, the IDF said an initial inquiry found that troops had identified a camera positioned by Hamas in the area of the hospital “used to observe the activity of IDF troops”, without providing evidence.

The IDF has not yet acknowledged carrying out more than one strike on the hospital, amid allegations from some international legal experts that it may have violated international law.

Intentionally carrying out attacks on civilians which are “excessive in relation to the concrete and direct military advantage anticipated” is prohibited under the Fourth Geneva Convention.

“A reasonable attacker must expect scores of civilian casualties since a hospital is full of protected persons,” Professor Janina Dill of Oxford University said.

Prof Dill added that the “mere presence of equipment that belongs to an adversary” does not mean a hospital or medical facility loses its protected status under the laws of war.

At least 247 journalists have been killed in Gaza since 7 October 2023, according to the UN, making it the deadliest conflict for reporters ever documented.

Israel’s military launched a campaign in Gaza in response to the Hamas-led attack on southern Israel on 7 October 2023, in which about 1,200 people were killed and 251 others were taken hostage.

Almost 62,900 people have been killed in Gaza in the same period, according to the Hamas-run health ministry.