UN humanitarian chief Martin Griffiths, who has played a key role in pressing for aid to Gaza and earlier led efforts on Yemen, is quitting due to ill health, the world body said Monday.

Griffiths, the under-secretary-general for humanitarian affairs and emergency relief coordinator, "has informed the secretary-general of his intention to step down for health reasons," UN spokesman Farhan Haq said.

Griffiths will remain in his position until the end of June to ensure a "smooth transition" to a since-undesignated successor, Haq said.

Griffiths, a British barrister, has repeatedly pressed for Israel to allow humanitarian assistance into the Gaza Strip as Israel wages a military campaign in response to the October 7 attack by Hamas.

Last month he warned Israel not to ignore calls against an assault in Rafah, where some 1.5 million Palestinians have taken shelter, warning that an Israeli operation "could lead to a slaughter."

Griffiths earlier served as UN special envoy for Yemen and has been an advisor on Syria. He has also worked for international humanitarian organizations including UNICEF, Save the Children and ActionAid.