John Ging, the high-profile director of the UN relief agency in Gaza, is to quit his current post to take up a senior UN job in New York.

Ging, 45, who has worked in Gaza since 2006, has been an enthusiastic and effective advocate for the rights of the Gazan population and a vocal critic of Israeli government policy.

He has been the target of assassination attempts and death threats in Gaza, and Islamist opponents have attacked projects he has promoted.

A charismatic former officer in the Irish army, Ging described the blockade of Gaza as a "medieval siege", and has said Israel's policies in the territory risk breeding a new generation of militants.

His departure from the United Nations Relief and Works Agency (UNRWA) will be welcomed by many in the Israeli political and military establishment who believe he overstepped the mark in his criticisms of their policies.

The director of UNRWA operations in the West Bank, Barbara Shenstone, also announced that she was leaving to return to her home country, Canada.

The agency said: "Barbara and John have made exceptional contributions to UNRWA's work under the most difficult circumstances."

The commissioner-general, Filippo Grandi, said: "Their commitment to ensuring the quality of UNRWA services has been extraordinary; their advocacy in support of rights has been outstanding – be it amidst heavy bombardment in Gaza during armed conflict or in responding to the abysmal rights abuses in the occupied West Bank."

Ging is to take up an unspecified role with the UN's Office for Coordination of Humanitarian Affairs.

No details were provided, but a UNRWA spokesman said it was "a big promotion".