A senior United Nations official who has been on a hunger strike in support of child victims of the Israel-Hamas conflict alleges he was assaulted by the organisation's security at its New York headquarters, an account the global body disputes.

A United Nations spokesperson said the official fell while forcibly resisting an attempt to remove him from the premises after he was refused permission to demonstrate there.

Bruno Donat, a 54-year-old senior U.N. humanitarian officer with U.S.-Mauritian citizenship, has been on a hunger strike since March 1 for child victims of the Israel-Hamas conflict. He halted his hunger strike on Tuesday, saying he was in pain and vomiting following the incident at the United Nations.

Donat, who works in the body's European office in Geneva and was previously employed on disarmament in the Democratic Republic of Congo, said he was barred entry when attempting to enter the building to meet a colleague late on Monday.

"They dragged me out," he told Reuters. "Outside, the security guy threw me on the ground and my head hit the pavement," he said. The incident caused bleeding, he said, and showed Reuters a picture of an injury to the back of his head that he said prompted him to be taken to hospital by ambulance.

He said he has reported the incident to U.N. management and planned to file a police report.

U.N. spokesperson Farhan Haq said Donat was repeatedly asked by security to leave and refused up until the building's closing time.

"At this point, he was ushered out by the officers on duty, during which he forcibly resisted their efforts to remove him from the premises, attempting to force his way back through the entry point," Haq said. "At this point, according to the officers, he fell backwards onto the path outside the main entrance."

Donat has been seeking to draw the world's attention to the thousands of children killed in Gaza during Israel's military campaign in response to Hamas' deadly Oct. 7 attacks. He has also called for the release of Israeli hostages in Gaza, including children.

Donat says his campaign outside the U.N. and on social media is a personal one.