Prime Minister Benjamin Netanyahu said Tuesday that the Israel Defense Forces had launched an investigation into the “disaster” that led to the deaths of 21 soldiers in Gaza the previous day.

“The IDF has launched an investigation of the disaster. We must learn the necessary lessons and do everything to preserve the lives of our warriors,” Netanyahu said in a statement on the incident, which made for the Israeli military’s deadliest single day in Gaza since the start of its ground operations on Oct. 27.

Netanyahu vowed Monday, after news of the soldiers’ deaths first came to light, that the IDF would continue its fight on until “absolute victory” over Hamas.

The 21 IDF reservists were killed when a militant fired a rocket-propelled grenade at a tank, setting off a secondary explosion that brought two buildings down onto the soldiers. They were among a total of 24 Israeli soldiers killed Monday in Gaza, which military spokesman Daniel Hagari confirmed had been the biggest single-day loss in almost three months of ground warfare.

Netanyahu on Monday mourned the loss, saying in a social media post that it had been “one of the hardest days since the outbreak of the war,” but adding: “In the name of our heroes, and for our own lives, we will not stop fighting until absolute victory.”

The IDF said on Tuesday, meanwhile, that soldiers had managed to completely encircle the southern Gaza city of Khan Younis, where much of the deadliest fighting and airstrikes have been focused in recent days. The Hamas-run Ministry of Health in Gaza said Tuesday that during the preceding 24 hours alone, 195 people were killed in the densely populated Palestinian territory.  

Israel accuses Hamas of operating from Al Nasser Hospital, the largest health facility in Khan Younis, and of basing some of its operations in the city.

Thousands of Palestinians who had sought shelter at the sprawling hospital have fled this week, with patients and displaced civilians describing relentless air and artillery strikes as IDF forces close in on the facility.

The Hamas-run health ministry says more than 25,400 people have been killed in Gaza since Israel launched its offensive in retaliation for the unprecedented Oct. 7 terror attack by the Palestinian militant group, which is designated a terrorist organization by Israel, the U.S. and the European Union. Hamas officials do not distinguish between combatant and civilian deaths. Israel says Hamas killed some 1,200 people with its October attack, and seized about 240 others as hostages.

About half of those hostages have been freed, but Israel says 132 are still believed to be held captive in Gaza. Pressure from the remaining hostages’ family members on Netanyahu’s government, to rescue their loved ones as a priority in the war, even if it means negotiating, has risen sharply. A group of family members stormed into a parliamentary meeting Monday and shouted angrily at lawmakers, demanding more be done to ensure that their loved ones come home.