The United Nations said one staff member was killed and another injured on the way to a hospital in southern Gaza on Monday.
Officials said they were on their way to the European Hospital near Rafah in a United Nations vehicle at the time of the attack.
The United Nations did not say who it believed was responsible for the attack.
The Israeli military said an initial investigation indicated the vehicle was hit in a combat zone and its path was not known.
Footage posted on social media and verified by the BBC shows a marked UN vehicle with multiple bullet holes outside the European Hospital.
The Israel Defense Forces (IDF) confirmed on Monday that it had received a United Nations Department for Security (UNDSS) report stating that two of its personnel were injured in the Rafah area in southern Gaza.
The IDF added that the incident is under review.
UN Secretary-General Antonio Guterres said he was “deeply saddened” to learn of the worker's death and offered his condolences to the family, his spokesman Farhan Haq said in a statement.
“The Secretary-General condemns all attacks on UN personnel and calls for a full investigation,” Haq added.
Haq said the killed and injured personnel were international staff, not Palestinians, adding that he believed it was the first death of an international UN staff member in Gaza since the start of the conflict.
Mr. Guterres said in a separate statement that more than 190 UN personnel have been killed in Gaza since the war began.
The staff killed on Monday is believed to be the United Nations' first international casualty, but an Israeli attack in early April killed six international aid workers and Palestinians from the international food charity World Central Kitchen. One colleague was killed.
Their deaths sparked an international outcry, and the IDF fired two senior officers, calling the incident a “serious accident.”
In response to a cross-border attack by Hamas on southern Israel on October 7, Israel launched a military operation in Gaza with the stated aim of annihilating Hamas, which controls Gaza, in which approximately 1,200 people were killed. and 252 other people were taken hostage.
More than 35,090 people have been killed in Gaza since then, according to the Hamas-controlled region's health ministry.