WHO chief Tedros Adhanom Ghebreyesus also said that such accusations couldendanger its staff on the ground.
Tedros was responding to claims made Thursday by Israeli ambassador MeiravEilon Shahar at a meeting of the UN health agency's board.
"WHO refutes Israel's accusation at the executive board meeting yesterdaythat WHO is in 'collusion' with Hamas and is 'turning a blind eye' to thesuffering of hostages being held in Gaza," Tedros said on X.
"Such false claims are harmful and can endanger our staff who are riskingtheir lives to serve the vulnerable.
"As a United Nations agency, WHO is impartial and is working for the healthand well-being of all people."
Earlier this month he told a press conference that healthcare should alwaysbe protected. It "cannot be attacked and it cannot be militarised", he said.
Eilon Shahar had said Hamas was embedding itself in hospitals in the GazaStrip and was using human shields in the Palestinian territory.
In "every single hospital that the IDF searched in Gaza, it found evidenceof Hamas' military use," she said Thursday.
"These are undeniable facts that WHO chooses to ignore time and time again.This is not incompetence; it is collusion.
"The WHO knew hostages were held in hospitals and that terrorists operatedwithin.
"Even when presented with concrete evidence of what was happening belowground and above ground ... WHO chooses to turn a blind eye, jeopardising thosethey are meant to protect."
- Situation 'beyond words' -
War erupted on October 7 when Hamas and other militants from Gaza launchedunprecedented attacks on Israel which claimed about 1,140 lives, according toan AFP tally of official Israeli figures.
Militants also seized 250 hostages, and Israel says around 132 remain inGaza. That number includes at least 28 dead hostages, according to an AFP tallybased on Israeli figures.
Israel, in response, launched a relentless military offensive that thePalestinian territory's health ministry says has killed at least 26,083 people.
On Thursday, Tedros was moved to tears as he addressed the executive board.
The fact that 70 percent of the fatalities in the Gaza Strip have been womenand children should be motive enough to bring about a "long overdue" ceasefire,he said.
"If we look for a solution it's always possible," he added, after pausingto compose himself. "It's only the will that's required."
Tedros occasionally becomes emotional when speaking about the impact of waron children, citing his own early years in Ethiopia.
"I am a true believer because of my own experience that war doesn't bringsolutions except more war, more hatred, more agony, more destruction," he saidThursday.
"I'm struggling to speak because... the situation is beyond words," hesaid, wiping his eyes.