The International Committee of the Red Cross (ICRC) says three of its workers have been killed, and two others injured in a strike in eastern Ukraine, BBC reports.
The ICRC did not identify who was behind the attack but called it "unconscionable" that "shelling would hit an aid distribution site".
Earlier, Ukraine's President Volodymyr Zelensky said those killed were Ukrainian and blamed Moscow for the shelling, calling it "another Russian war crime".
The agency said its vehicles are clearly marked and operate regularly in the frontline region of Donetsk.
"I condemn attacks on Red Cross personnel in the strongest terms," said the agency's president Mirjana Spoljaric, adding that: "Our hearts are broken today as we mourn the loss of our colleagues and care for the injured."
The ICRC said its team had been preparing to distribute wood and coal briquettes to homes in Viroliubivka village, north of Donetsk city, when it was hit.
The distribution of the goods had not begun yet and no residents were affected by the explosion, the agency said.
It did not confirm any details about the identities of those killed.
Earlier, Ukrainian officials had reported shelling in Viroliubivka and said workers had been unloading supplies when the attack happened.
In a post on social media, Ukraine's leader blamed a Russian strike. Zelensky shared a photo of a white truck in flames branded with the Red Cross logo on its side.
"Today, the occupier attacked the vehicles of the International Committee of the Red Cross humanitarian mission," he said.
The Ukrainian ombudsman Dmytro Lubinets also commented online, urging the Red Cross to publicly attribute the attack to Russia.
"The shelling is already known about, but the ICRC... remain silent!" he wrote.
In its statement, the ICRC had reiterated that it is a "neutral, impartial and independent organisation with an exclusively humanitarian mandate".
It deplored the "sharp rise" in the killings of humanitarians around the world in the past two years.
The United Nations has also made similar warnings. Its humanitarian mission to Ukraine earlier this year said 50 workers had killed or injured in Ukraine in 2023, including 11 killed in the line of duty, reported AFP news agency.
