At least 20 people, including five journalists working for the international media, have been killed in an Israeli double strike on Nasser hospital in Khan Yunis in southern Gaza, the territory’s Hamas-run health ministry says.

The journalists had worked with Reuters, AP, Al Jazeera and the Middle East Eye, the news outlets confirmed.

Four health workers were also killed, the World Health Organization’s chief said.

Footage of the attack shows a second strike hitting rescuers who had arrived to help those targeted by the initial attack.

Israeli Prime Minister Benjamin Netanyahu called the incident a “tragic mishap” and said military authorities were “conducting a thorough investigation”.

The latest deaths brings the number of journalists killed in Gaza since the start of the war there in October 2023 to nearly 200.

According to the Committee to Protect Journalists (CPJ), a leading body which promotes press freedom, the war in Gaza has been the deadliest conflict for journalists ever documented. It says more press members have been killed there in the past two years than were killed worldwide in the prior three years.

International journalists have been banned by Israel from entering the Gaza Strip independently since the start of the war.

Some journalists have been taken into Gaza by the Israel Defense Forces (IDF) under controlled access, but international media outlets rely on local reporters for much of their coverage in Gaza.

• Israeli double strike on Gaza hospital – what we know

Video from the scene of Monday’s attack shows a doctor standing at an entrance to the hospital – the main one in southern Gaza – holding up bloodied clothes to show journalists following the first strike. Suddenly there is a blast, sending people running for cover as glass shatters. A man injured by the blast is seen trying to drag himself to safety.

Another graphic video, captured on a livestream by al-Ghad TV, shows several emergency workers responding to the first strike near the top floor of Nasser hospital as a number of journalists in the background capture the scene.

A staircase, where journalists often gather to get views across Khan Younis, is visible in the footage. A strike then directly hits the emergency workers and journalists, sending smoke and rubble in the air. At least one body is visible in the aftermath.

Reuters news agency said its cameraman, Husam al-Masri, was among those killed. He had been operating a live TV feed on the roof and it shut down at the instant of the initial strike. Hatem Khaled, another contractor also working for Reuters as a photographer, was injured in the second strike, according to witnesses.

The agency said it was devastated and “urgently seeking more information”.

AP said Mariam Dagga, a freelance journalist working for it, was also killed. The news agency said it was “shocked and saddened” by the 33-year-old’s death.

The others killed were Al Jazeera’s Mohammad Salama, Middle East Eye freelancer Ahmed Abu Aziz and photographer Moaz Abu Taha. US TV network NBC said Taha did not work for it, as had been initially reported. Reuters said he had worked with several news organisations, including Reuters.

The Hamas-run Civil Defence said one of its members was among those killed, AFP news agency reported.

Hadil Abu Zaid, a programme officer for British-based charity Medical Aid for Palestinians, said in a statement sent to media that she was visiting the ICU “when explosions tore through the operating theatre right next to us”.

“The killed and injured were everywhere,” she said, adding that the scene was “unbearable”.

There has been swift condemnation of the strike.

“These latest horrific killings highlight the extreme risks that medical personnel and journalists face as they carry out their vital work amid this brutal conflict,” UN Secretary General António Guterres said.

He demanded “a prompt, and impartial investigation” in addition to “an immediate and permanent ceasefire”.

Philippe Lazzarini, who heads Unrwa, the UN’s Palestinian refugee agency, expressed outrage at the killing of more journalists, which he said was “silencing the last remaining voices reporting about children dying silently amid famine”.

UK Foreign Secretary David Lammy said he was “horrified” by the deadly strike, which French President Emmanuel Macron called “intolerable”.

Monday’s attack comes two weeks after six journalists, including four from Al Jazeera, were killed in an Israeli targeted attack near al-Shifa Hospital in Gaza City.

The Hamas-run health ministry in Gaza said on Monday that the bodies of 58 people who had been killed in Israeli attacks had reached Gaza’s hospitals over the past day, with more bodies unreachable under the rubble of destroyed buildings.

The ministry said the dead included 28 people who were killed while trying to access food aid at distribution sites.

Hospitals also recorded a further 11 deaths due to malnutrition, the ministry said, including two children, bringing the total number of such deaths to 300 including 117 children.

The war was triggered by the Hamas-led attack on Israel on 7 October, in which about 1,200 people were killed and 251 others taken to Gaza as hostages.

Israel responded with a massive military offensive, which has killed more than 62,744 Palestinians, according to figures from the health ministry, which the UN considers reliable.