A senior United Nations official has issued an unprecedented appeal to British MPs to use their influence to try to alleviate the impact of "indiscriminate" and "illegal" Israeli sanctions in Gaza which display "profound inhumanity" and are "serving the agenda of extremists".

In one of the strongest attacks on recent Israeli strategy issued by a senior international official, John Ging, Gaza's director of operations for the refugee agency UNRWA, said that "crushing sanctions" imposed since the Israeli cabinet declared the Strip a "hostile entity" in September had contributed to "truly appalling living conditions."

Mr Ging said the measures had been justified as protection from what he fully acknowledged were rocket attacks "terrorising" the Israeli civilian population within range. The rockets have killed two people this year and injured 99 others. But citing cuts in fuel and planned cuts in electricity along with closures which have had "an atrocious" impact on Palestinian medical care, "destroyed" Gaza's economy and threatened already "Third World" water and sanitation, he told the Britain-Palestine group of MPs: "This presupposes that the civilian population are somehow more capable of stopping the rocket fire than the powerful military of the occupying power.

"My message ... is that not only are these sanctions not working, but because of their profound inhumanity, they are counterproductive to their stated purpose and while Gaza is not yet an entity populated by people hostile to their neighbour, it inevitably will be if the current approach of collective punitive sanctions continues."

Mr Ging, whose agency is responsible for 70 per cent of Gaza's 1.5 million population, said that over the past two years "every hopeful opportunity has been irrationally dashed and followed by even worse circumstances". He added that Gaza's civilian population expected more of Israel and the international community, who regularly expressed concern about their humanitarian plight but "to no avail".

Mr Ging, whose message is reinforced by a letter warning of the "increasingly desperate situation" in Gaza from major aid agencies in today's Independent, said 649 Palestinians had been killed this year, including 63 children. The figure includes more than 330 killed in internal fighting.

Mr Ging added that UNRWA was unable to provide more than 61 per cent of the necessary calories to refugees. "At present we do not have sufficient funding to provide just one high nutrient biscuit to 200,000 children in UN schools."

Israeli officials cite signs of a decline in Hamas's popularity as evidence that the sanctions are working. But Mr Ging said the "human suffering and misery for the entire civilian population in Gaza was creating fertile ground for the extremists".

The Israeli branch of Physicians for Human Rights says that 11 patients have died since last month because their treatment was blocked or delayed. At least 800 more are being denied treatment abroad.