Aid workers including an Australian and two people said to be British and Polish have been killed in Gaza, in what their charity founder said was an Israeli attack.
World Central Kitchen (WCK) founder and chef José Andrés said his staff had been killed "in an IDF air strike".
Gaza's Hamas-run media office also blamed Israel. The alleged strike could not be verified independently.
Israel's military said it was conducting a "thorough review".
A journalist working for the BBC in Gaza has seen the bodies of three international aid workers and a Palestinian driver, recovered from the site of the alleged air strike. Foreign passports were also shown.
The group are said to have been involved in co-ordinating the arrival of another boat carrying food aid to central Gaza.
Adrienne Watson, a spokesperson for the White House National Security Council, said on X: "We are heartbroken and deeply troubled by the strike that killed [WCK] aid workers in Gaza.
"Humanitarian aid workers must be protected as they deliver aid that is desperately needed, and we urge Israel to swiftly investigate what happened."
A medical source at al-Aqsa hospital in the central Gaza Strip told the BBC that the bodies of the four workers and their Palestinian driver had been brought to the hospital after a car they were travelling in on the coastal road was hit by an air strike at Deir al-Balah.
Further details of the alleged attack are still emerging.
Australian Prime Minister Anthony Albanese has confirmed that aid worker Lalzawmi "Zomi" Frankcom was among those killed and has offered his condolences to family and friends.
In a statement, he said: "This is someone who was volunteering overseas to provide aid through this charity for people who are suffering tremendous deprivation in Gaza. And this is just completely unacceptable."
He said Australia expected "full accountability", adding that it was a "tragedy that should never have occurred".
A Palestinian medical source told the BBC the workers had been wearing bullet-proof vests bearing the WCK logo. The charity is currently providing meals for thousands of people in Gaza.
In a statement, the WCK said it was "aware of reports" that members of its team had been "killed in an IDF [Israel Defense Forces] attack while working to support our humanitarian food delivery efforts in Gaza".
"This is a tragedy. Humanitarian aid workers and civilians should never be a target, ever. We will share more information when we have gathered all the facts," it added.
In a post on X, Mr Andrés, a celebrity chef, called on the Israeli government "to stop this indiscriminate killing".
The charity recently made headlines for providing hundreds of tonnes of food for Gazans that arrived on the first aid ship.
Commenting on the reports, the IDF said it was conducting a thorough review at the highest level to understand the circumstances of this "tragic incident".
"The IDF makes extensive efforts to enable the safe delivery of humanitarian aid, and has been working closely with WCK in their vital efforts to provide food and humanitarian aid to the people of Gaza," it added.
Prior to confirmation that an Australian national had been killed in the incident, the Australian foreign ministry said: "We have been very clear that we expect humanitarian workers in Gaza to have safe and unimpeded access to do their lifesaving work".
The UK Foreign Office and Polish foreign ministry have been contacted for comment.
Credit: BBC