The Israeli army said that 21 soldiers have been killed in the central Gaza Strip, marking the deadliest single incident for the troops in the more than three-month-old war against Hamas militants.

Army spokesman Daniel Hagari, speaking after a news blackout was lifted on Tuesday morning, said the soldiers were killed on Monday afternoon when two nearby buildings exploded and collapsed.

The blasts were likely the result of mines that had been planted by the troops to demolish the structures, Hagari said, while cautioning that it was not clear what triggered the blasts and that this was still under investigation.

Palestinians had fired a rocket at a tank being used by the soldiers around the same time as the buildings collapsed, adding to the confusion over what occurred.

Hagari said the Israel Defense Forces (IDF) has informed the families of all those affected.

Israeli President Isaac Herzog called it an “unbearably difficult morning” and described the fallen soldiers as heroes.

“The intense battles are taking place in an extremely challenging space, and we are strengthening the soldiers of the IDF and the security forces who are working with endless determination to realise the goals of the fighting,” Herzog wrote on X, formerly Twitter.

Fierce fighting has intensified in particular in the area around the southern city of Khan Younis.

Israel suspects the leadership of Hamas and many Israeli hostages remain in the tunnel network.

According to military figures, 220 soldiers have been killed since the start of the Israeli ground offensive in the Gaza Strip at the end of October.

More than 1,200 others have been injured.

The war was triggered by the worst massacre in Israel’s history, carried out by terrorists from the Palestinian group Hamas and allied extremists.

About 1,200 people were killed in the attack on southern Israel, including hundreds of soldiers.

The Palestinian death toll from the war between Israel and Hamas tops 25,000, with a further 63,000 people injured, according to the Hamas-run Health Ministry in Gaza.