Israeli military spokesman Rear Admiral Daniel Hagari said 21 soldiers were killed in an explosion when two buildings they had mined for demolition collapsed after militants fired grenades at a nearby tank.
Earlier, the military said three soldiers were killed in a separate attack in southern Gaza.
"Yesterday we experienced one of our most difficult days since the war erupted," Israeli Prime Minister Benjamin Netanyahu said. "In the name of our heroes, for the sake of our lives, we will not stop fighting until absolute victory."
Defence Minister Yoav Gallant said the war would determine Israel's future "for decades to come".
"The fall of the fighters is a requirement to achieve the goals of the war," Gallant said.
The deaths came as Israeli forces mount their biggest ground campaign of the new year, pushing deep into the western part of Khan Younis, the main city in the south of the Palestinian enclave, near areas sheltering hundreds of thousands of people who fled other parts of the enclave.
Gazans say Israeli blockades and storming of hospitals since Monday left the wounded and dead beyond the reach of rescuers as fighting escalated in the crowded city.
The dead were being buried inside the grounds of Khan Younis's main Nasser hospital because it was unsafe to leave to reach the cemetery. Another Khan Younis hospital, Al-Khair, was stormed by Israeli troops who arrested staff there, and a third, Al-Amal, where Red Crescent rescuers are based, was cut off and unreachable, according to Palestinian officials.
Israel says Hamas fighters operate in and around hospitals, making them legitimate targets. Hospital staff and Hamas deny this.
Israel has vowed to wipe out Hamas, the Palestinian Islamist movement that rules Gaza and is sworn to Israel's destruction, whose fighters stormed across the fence into Israel, killing 1,200 people and abducting around 250 hostages on Oct. 7.
At least 25,295 Gazans have since been confirmed killed, according to Palestinian authorities, with thousands more dead feared lost in the rubble, in Israel's campaign, which has laid most of the enclave to waste.
Nearly all of Gaza's 2.3 million people have lost their homes, the vast majority now penned into small towns just north and south of Khan Younis, many sleeping rough in makeshift tents with food and medicine running out and no clean water.
The large death toll of Israeli troops in fighting comes at a time when Israel itself is beginning to see the first stirrings of discontent with Netanyahu's war strategy - committed to the total annihilation of Hamas but with only vague discussion of what would come next for Gaza.
Since last week, Netanyahu has vowed never to let Palestinians have an independent state, a break with Israel's main ally Washington which has considered a peace process ultimately leading to a Palestinian state as the bedrock of its Middle East policy for decades.
Relatives of hostages still held in Gaza have called for more effort to bring them home, even if that means reining in the military campaign. A group of them burst into a parliamentary committee hearing on Monday.
Last week, a member of Netanyahu's war cabinet, former military chief-of-staff Gadi Eisenkot, whose own soldier son was killed in the ground offensive in Gaza, said the campaign had yet to achieve its aims of dismantling Hamas and there was no hope of freeing the hostages in a military operation.
He called for swift elections to replace a government he said had lost public confidence.
The conflict has been accompanied by an escalation in violence elsewhere in the Middle East, especially where armed groups allied to Israel's arch foe Iran operate, including Lebanon, Iraq, Syria and Yemen.
The Iran-aligned Houthi movement, which controls most of the populated parts of Yemen, has attacked shipping in the Red Sea in what it says is support for Gaza. The United States and Britain, which have been striking the Houthis this month, carried out another round of air strikes overnight.
