Twenty-one Israeli soldiers were killed during fighting in southern Gaza on Monday, in the biggest single loss of life for Israeli troops inside the battered enclave since the war with Hamas began.

Iran PressIran News: In a televised statement Tuesday, Israeli Occupation Forces (IOF) spokesperson Daniel Hagari said a tank that was protecting Israeli troops was hit by a rocket-propelled grenade (RPG).

Israeli media reported that two soldiers in the tank were killed.

Simultaneously, two two-story buildings collapsed on soldiers following an explosion. Most of the Israeli forces killed were in or near the buildings, he said.

“The buildings probably exploded because of the mines that our forces laid there, in preparation to demolish them and the infrastructure around,” Hagari said.

The IDF spokesperson told CNN Tuesday that it is “still not clear” what caused the building explosion.

All families have been notified but only 10 names have been released so far, he said.

Another Israeli force was seriously injured in the same incident, Hagari added.