By Chris McGreal

The Bush administration has blocked the reappointment of the UN's Palestinian refugee agency chief, Peter Hansen, after a campaign by conservative and Jewish groups in the US, and the government in Jerusalem which accused him of being an "Israel hater".

Some European and Arab governments were keen for Mr Hansen to stay on at the end of his nine-year tenure but the US supported Israel's assertion that the head of the UN Relief and Works Agency (UNRWA) is biased and soft on "terrorists". This week Mr Hansen sent an email to staff saying he will leave on March 31.

Yesterday, the UNRWA chief declined to discuss his failure to be reappointed but did say he believes politically motivated opposition played a role in his removal. "I was willing to stay. There are certain facts about the views of certain groups in the US and Israel about how I have carried out my functions and those groups influenced the decision not to reappoint me," he said.

Mr Hansen infuriated the Israeli government with public criticisms of the military's wholesale destruction of Palestinian homes which he described as a grave breach of international humanitarian law. He also spoke out against the killing of children by indiscriminate Israeli gunfire hitting UN-run schools, and Israeli policies that have contributed to economic collapse and growing hunger among about 1m refugees in Gaza.

The Israeli ambassador to the UN, Dan Gillerman, often attacked Mr Hansen, saying he was exceeding his remit and calling him an "Israel hater". Pro-Israel groups in the US, such as the World Jewish Congress and the America Israel Public Affairs Committee, lobbied strongly against him.

Late last year, a US congressman, Tom Lantos, met the UN secretary general, Kofi Annan, and told him the Bush administration wanted Mr Hansen out. A UN source said that at a meeting in New York last month, Mr Annan told Mr Hansen: "I don't have the political capital with the Americans to keep you." Mr Annan has been under pressure from US conservatives demanding his resignation over corruption in the UN's oil for food programme in Iraq.

Mr Hansen said Mr Gillerman's description of him was "outrageous". "I don't have a record of being an Israel hater but I can't in all honesty not criticise Israel's actions that harm Palestinian refugees," he said. "My job is not to put myself at the midpoint between the Israeli view and the refugees' view. My job was to represent the refugees."

Mr Hansen came under political attack twice toward the end of last year. The Israeli army erroneously claimed that its spy drones had recorded Palestinian fighters loading a rocket into the back of a UN ambulance. The Israeli government launched a vigorous international campaign based on the video to portray UNRWA as working with terrorists but the military was later forced to admit that, as Mr Hansen insisted, the "rocket" was really a stretcher.

Mr Hansen was more vulnerable after he told a Canadian radio station that his organisation employed members of Hamas. "It would have been outright dishonest to say that among a population with about 30% support for Hamas that none of them worked for us," he said yesterday. But his statements were widely used by opponents to claim that UNRWA was a haven for terrorists.

An Israeli foreign ministry spokesman, Mark Regev, said the government hoped that Mr Hansen's departure would improve relations with UNRWA. "Our relationship with Hansen was complex and ... difficult. His statements were one-sided and some of his actions were problematic," he said.