Reuters, the Associated Press and Al Jazeera all issued statements mourning their slain contributors, while the Israeli military said it would investigate the incident.

The ongoing war in Gaza has been one of the deadliest for journalists, with around 200 media workers killed over the course of the nearly two-year Israeli assault, according to media watchdogs.

Civil defense spokesman Mahmud Bassal said "the toll so far is 20 martyrs, including five journalists and one member of the civil defense", after strikes hit Khan Yunis's Nasser Hospital -- a large medical complex that has been targeted several times by Israel since the start of the war.

In a statement, the Israeli military said its troops had "carried out a strike in the area of Nasser Hospital".

"The Chief of the General Staff instructed to conduct an initial inquiry as soon as possible," it said, adding it "regrets any harm to uninvolved individuals and does not target journalists as such".

Bassal said an Israeli explosive drone hit a building at the hospital, followed by an air strike as the wounded were being evacuated.

Netanyahu said in a statement Monday evening that his country "deeply regrets the tragic mishap that occurred today at the Nasser Hospital".

"Israel values the work of journalists, medical staff, and all civilians," he added. 

Reuters reported that video journalist Hussam al-Masri -- a contractor who was working for the agency -- was operating a live feed at the hospital, "which suddenly shut down at the moment of the initial strike".  

'Devastated'

A Reuters spokesperson said the agency was "devastated" to learn of Masri's death "and injuries to another of our contractors, Hatem Khaled" in the strikes.

"We are urgently seeking more information and have asked authorities in Gaza and Israel to help us get urgent medical assistance for Hatem," the statement added.

A spokesperson for Qatar-based TV network Al Jazeera said one of its photojournalists and cameramen, Mohammad Salama, was also killed in the attack.

"Al Jazeera Media Network condemns, in the strongest possible terms, this horrific crime committed by the Israeli occupation forces, who have directly targeted and assassinated journalists as part of a systematic campaign to silence the truth," the broadcaster said in a statement. 

The Associated Press said in a statement that it was "shocked and saddened" to learn of the death of Mariam Dagga, 33, a visual journalist who had freelanced for the agency since the start of the war.

The Palestinian Journalists Syndicate named two other victims as Moaz Abu Taha and Ahmad Abu Aziz.

Later Monday, a sixth journalist, Hassan Douhan, was killed by Israeli fire in the Al-Mawasi area of Khan Yunis, according to the Palestinian Journalists Syndicate and Nasser Hospital. 

Smoke, bloodied bodies

Media restrictions in Gaza and difficulties in accessing many areas mean AFP is unable to independently verify the tolls and details provided by the civil defense agency or the Israeli military.

AFP footage from the immediate aftermath of the attack showed smoke filling the air and debris from the blast on the floor outside the hospital.

Palestinians rushed to help the victims, carrying bloodied corpses and severed body parts into the medical complex. One body could be seen dangling from the top floor of the targeted building as a man screamed below.

A woman wearing medical scrubs and a white coat was among the injured, carried into the hospital on a stretcher with a heavily bandaged leg and blood all over her clothes. 

Nasser Hospital is one of the last remaining health facilities in the Gaza Strip that is at least partially functioning.

Later in the day, a crowd carried the bodies of some of the slain journalists at a funeral in Khan Yunis, with the dead wrapped in white burial shrouds and their press flak jackets resting on top. 

"We will not stop walking this path, and the coverage will continue, God willing," said Masri's brother Mahmoud. 

'Immediate explanation'

The strike was condemned by a range of voices, including the UN, media outlets, rights groups and the Israel-based Foreign Press Association. 

Earlier this month, four Al Jazeera staff and two freelancers were killed in an Israeli air strike outside Al-Shifa hospital in Gaza City, prompting widespread condemnation.

The Israeli military alleged that Anas al-Sharif -- a prominent Al Jazeera correspondent killed in the strike -- headed a Hamas "terrorist cell" and was "responsible for advancing rocket attacks" against Israelis.

The war in Gaza was sparked by Hamas's October 2023 attack on Israel, which resulted in the deaths of 1,219 people, mostly civilians, according to an AFP tally based on official figures.

Israel's retaliatory offensive has killed at least 62,744 Palestinians, most of them civilians, according to figures from the health ministry in Hamas-run Gaza that the United Nations considers reliable.