(JNS) Twenty-one soldiers were killed in central Gaza on Monday when two buildings collapsed due to a blast, Israel Defence Forces Spokesperson Daniel Hagari said on Tuesday morning.

An additional three soldiers were killed in combat as part of a stepped-up assault on the southern Gaza city of Khan Younis.

It was the deadliest day since the start of the ground offensive against Hamas in Gaza.

The incident occurred 600m from the Israeli border near the northwestern Negev community of Kibbutz Kissufim as Israeli forces were working on clearing Hamas infrastructure and buildings to establish a buffer zone.

According to Hagari, at around 4pm terrorists fired a rocket-propelled grenade at a tank securing the forces. At the same time, two two-story buildings collapsed as a result of an explosion while most of the troops were inside or near them.

The blast was apparently caused by explosives planted by the Israeli forces, intended to destroy the buildings in a controlled event.

Hagari emphasised that the incident is still under investigation, including the cause of the explosion.

He added that a “very complicated” rescue operation took place involving commanders and rescue workers who arrived quickly to the scene.

“War has a very painful and heavy price. The dedicated reservists, who stood up for the flag, sacrificed the most precious of all, for the security of the State of Israel and so that we can all live here safely,” said Hagari.

Israeli Prime Minister Benjamin Netanyahu called it “one of the most difficult days since the outbreak of the war,” saying that he was sending strength to the bereaved families.

“I mourn for our fallen heroic soldiers. I hug the families in their time of need and we all pray for the peace of our wounded,” the premier continued, adding that the IDF had launched an investigation into the incident.

“We must learn the necessary lessons and do everything to preserve the lives of our warriors. In the name of our heroes, we will not stop fighting until absolute victory,” said Netanyahu.

Israeli President Isaac Herzog on Tuesday called it “an unbearably difficult morning, in which more and more names of the best of our sons…are added to the gravestones of heroes”.

Herzog continued: “Behind every name is a family whose world has fallen, a family whose pain and sorrow we feel in our hearts. At the same time, we feel pride for the heroism of our generation, for the mission to combat evil, for sticking to the goal and for the love of our people and homeland.”

Israeli Defence Minister Yoav Gallant said that “our hearts are with the dear families in their most difficult time,” adding: “This is a war that will determine the future of Israel for decades to come – the fall of the soldiers compels us to achieve the goals of the fighting.”

The IDF initially released for publication the names of 10 of the soldiers killed in the incident. The families of the remaining 11 were notified, and the military later in the morning allowed for publication the names of seven additional soldiers. The military will release the names of the remaining four soon.

A total of 210 soldiers have been killed since the start of Gaza ground operations on October 27, and 545 have been killed on all fronts since the start of the war on October 7.