The United Nations' former top Middle East envoy has sharply criticized U.S. and Israeli efforts to isolate the Hamas-led Palestinian government, saying the policy has further radicalized Palestinian opinion and undercut long-term efforts to establish a viable Palestinian state.

The broadside by Alvaro de Soto was contained in a confidential 52-page report he filed before resigning from the United Nations last month, ending a 25-year U.N. career. It was an unusually candid assessment by the Peruvian diplomat, who has overseen U.N. peace efforts in El Salvador, Cyprus, Western Sahara and other trouble spots.

Starting in May 2005, de Soto directed U.N. efforts to ease the Israeli-Palestinian conflict during a turbulent period that included the withdrawal of Israeli forces from the Gaza Strip, the electoral victory that gave Hamas control of the Palestinian Authority, and the departure of an ill Ariel Sharon, then the prime minister, from the political scene.

The report charged that U.N. Secretary General Ban Ki Moon and predecessor Kofi Annan provided political cover for U.S. and European efforts to quarantine Hamas. De Soto accused Annan of "hampering" peace efforts by prohibiting him from maintaining regular diplomatic contacts with Hamas leaders.

De Soto also criticized the Palestinian leadership. He referred to Hamas's charter, which advocates the destruction of Israel, as "abominable," and said that Palestinian efforts to stop violence against Israel are "patchy at best, reprehensible at worst." De Soto advised Ban to reconsider the United Nations' membership in the Quartet -- a diplomatic grouping that includes the United States, the European Union and Russia -- saying it has provided a political "shield" for U.S. and European efforts to bankrupt the Palestinian government.

De Soto said that the Quartet has grown increasingly biased in favor of Israel over the past two years. He said that it made a strategic mistake by imposing conditions on Hamas after its January 2006 electoral victory -- that it renounce violence, recognize Israel and embrace prior peace agreements.

"Even handedness has been pummeled into submission," De Soto said in the report, which was first reported by London's Guardian newspaper and posted on its Web site. "The Quartet took all pressure off Israel. With all the focus on the failings of Hamas, the Israeli settlement enterprise and barrier construction has continued unabated."

But Ban defended his approach. "The Quartet, I think, has been contributing a lot to the peace and security in Middle East," he said.

De Soto said that American prestige in the Arab world is at "historically low levels" and that U.S. officials "clearly pushed for a confrontation" between Hamas and Fatah, the secular movement that backs the pro-Western Palestinian President Mahmoud Abbas.

De Soto described a Quartet meeting on the eve of the February Palestinian peace talks in Mecca, Saudi Arabia, which were aimed at ending the fighting between the two Palestinian factions. A U.S. representative, he recalled, said: "I like this violence . . . it means that other Palestinians are resisting Hamas."

De Soto also accused Secretary of State Condoleezza Rice and other senior U.S. officials of having "hijacked" efforts by former Quartet envoy James D. Wolfensohn to negotiate an agreement to provide greater freedom of movement for civilians in Gaza and the West Bank.

De Soto portrayed Sharon as a brilliant political tactician who boosted Israel's international standing by deciding to withdraw Israeli troops from Gaza. In exchange, he extracted President Bush's written endorsement of Israel's opposition to the return of Palestinian refugees to Israel and of large Israeli settlement blocs in the West Bank.

De Soto characterized Israel's current prime minister, Ehud Olmert, as a "weak" leader. He accused him of maintaining an economic vise grip on the Palestinian Authority by withholding tax revenue that Israel collects on its behalf. "He has done little, grudgingly and late, to strengthen his hand," he said.