calling it new evidence of Hamas exploitation of what is known as UNRWA, the U.N. relief group that aids Palestinians.

Israeli army engineers took reporters from foreign news outlets through the passages during what is a time of crisis for UNRWA.

Israel last month alleged that some of the agency's staff doubled as Hamas operatives, which led several donor countries to freeze their funding to the agency.

UNRWA has launched an internal investigation into Israel's claims.

The tunnels, under the agency's headquarters in Gaza City, also revealed side-rooms, including an office space with steel safes that had been opened and emptied. One large chamber was packed with computer servers, another with industrial battery stacks.

Leading the tour was an Israeli lieutenant-colonel, who gave only his first name, Ido.

"This is one of the central commands of the intelligence. This place is one of the Hamas' intelligence units, where they command most of the combat from here, from the underground."

Ido said Hamas appeared to have evacuated in the face of the Israeli advance, preemptively cutting off communications cables that, in an above-ground part of the tour, he showed running through the floor of the UNRWA basement.

The Palestinians have accused Israel of falsifying information to tarnish UNRWA, which employs 13,000 people in the Gaza Strip and for years has been a lifeline for the population, running schools, healthcare clinics and other social services.

In a statement, UNRWA said it had vacated the headquarters on Oct. 12, five days after the war began, and was therefore (quote) "unable to confirm or otherwise comment" on the Israeli finding.

Hamas has denied operating in civilian facilities.

As a condition of taking journalists on the trip, the Israeli military requested approval of photos and video before they were transmitted.