Israel's foreign minister called Saturday for the head of the UN agency for Palestinian refugees to quit, following Israeli claims that a Hamas tunnel had been discovered under its evacuated Gaza City headquarters.
Israel Katz dismissed UNRWA commissioner general Philippe Lazzarini's claim that he was unaware of its presence as "not only absurd but also an affront to common sense".
"His prompt resignation is imperative," he wrote on X, formerly Twitter.
Lazzarini, already under pressure after Israel claimed some UNRWA staff were involved in the October 7 Hamas attack, said the agency had not operated from the compound since October 12.
Instead he called for an independent investigation.
Hamas has previously denied Israeli claims that it has dug an extensive network of tunnels under schools, hospitals and other civilian infrastructure as cover for its activities.
Israel's army and the Shin Bet security agency said operations in Gaza City in recent weeks had led to the discovery of a "tunnel shaft" near a school run by the humanitarian agency.
"The shaft led to an underground terror tunnel that served as a significant asset of Hamas's military intelligence and passed under the building that serves as UNRWA's main headquarters in the Gaza Strip," they added in a statement.
"Electrical infrastructure" in the tunnel -- 700 metres (765 yards) long and 18 metres underground -- "connected" to the agency's HQ, "indicating that UNRWA's facilities supplied the tunnel with electricity", they said.
Documents and a stash of weapons in the UN compound itself "confirmed that the offices had in fact also been used by Hamas terrorists", the joint statement said.
Katz claimed the discovery showed UNRWA's "deep involvement" with Hamas.
An AFP photographer was among a number of journalists taken to the compound and tunnel by the Israeli military on Thursday.
UN premises are considered "inviolable" in international law and immune from "search, requisition, confiscation, expropriation and any other form of interference".
Lazzarini wrote on X that its staff were forced to leave its Gaza City compound under instruction from Israeli forces as bombardment intensified in the area and had not returned.
"We have not used that compound since we left it nor are we aware of any activity that may have taken place there," he added.
The compound was last inspected in September 2023, he said.
Any suspicious "cavity" found near or under any UNRWA premises was previously reported to the authorities in Hamas-controlled Gaza and the Israelis, and also made public, he said.
The latest claims "merit an independent inquiry that is currently not possible to undertake given Gaza is an active war zone", he added.
"The Israeli authorities have not informed UNRWA officially about the alleged tunnel." Instead the agency learned about it from media reports, he said.
The UN has launched two separate probes into UNRWA, the first into Israeli claims that 12 of its staff may have participated on October 7, and the other a review of its overall political neutrality.
UN chief Antonio Guterres has spoken out in defence of the agency, calling it the "backbone" of Gaza aid.
So too has US Secretary of State Antony Blinken, who said it played an "absolutely indispensable role in trying to make sure that men, women and children who so desperately need assistance in Gaza actually get it."
