Geneva, Switzerland - The outgoing head of the United Nations agency supporting Palestinian refugees said on Tuesday he wanted an investigation into the killing of nearly 400 UNRWA staff during Israel's Gaza siege.

"I believe that we need to have a panel... a high-level panel of experts to look into the killing of our staff," Philippe Lazzarini told reporters in Geneva.

Speaking at a press conference on the last day on the job as UNRWA Commissioner-General, the 62-year-old Swiss national condemned the fact that "more than 390" of the agency's staff had been killed since the start of Israel's war on Gaza in October 2023.

"Many others have sustained life-changing injuries or have been arbitrarily detained and tortured," he said.

Lazzarini said an investigation was needed not just into the killing of UNRWA employees but also of other UN staff, stressing: "There have been other UN colleagues who have been also killed."

"And we have to look also at the extraordinary, large-scale destruction of the agency, of UN premises in Gaza," he added.

Lazzarini has warned that Israeli attacks on the agency, coupled with severe funding cuts, have left UNRWA facing "collapse."

He said he had raised the issue of an investigation with the office of UN Secretary-General Antonio Guterres and with UN member states in New York.

The question, Lazzarini said, was "when is the right time to start this, as... everything in this context is polarized."

"The more time goes, the more difficult the task for the commission will be in the future."

Israel has killed at least 72,000 people in Gaza since October 2023, according to the territory's health ministry. There is wide consensus among human rights and legal experts that Israel has committed genocide and ethnic cleansing in Gaza.