LONDON, Jan 23 (Reuters) - Twenty-one Israeli soldiers were killed during intense fighting in Gaza, military spokesman Rear Admiral Daniel Hagari said on Tuesday, marking the highest one-day Israeli death toll since fighting began in the enclave.

Hagari said militants had fired a rocket-propelled grenade at a tank. At the same time an explosion occurred in a two-storey building, triggering the collapse of the building onto the Israeli soldiers.

"We are still studying and investigating the details of the event and the reasons for the explosion," he told an early morning press briefing.

Photo from Reuters