GAZA CITY, Gaza Strip - Prime Minister Ismail Haniyeh of Hamas said Friday he hopes to form a new coalition government with Fatah moderates in less than three weeks, despite unresolved internal disputes and a reported warning of a U.S. boycott.

In quick succession Thursday, Haniyeh and his government resigned and President Mahmoud Abbas of Fatah appointed him to form the new team, based on last week's agreement in the Muslim holy city of Mecca to split power between the two rivals.

Haniyeh has five weeks to put together a new Cabinet. During that period, Hamas and Fatah need to resolve deep disputes over control of the security forces and whether to dismantle a separate Hamas militia.

At a sermon Friday at a Gaza City mosque, Haniyeh said he hoped to form a new government well before the deadline.

"We hope the government will be produced in less than three weeks and presented to the esteemed parliament" for approval, he said.

However, even if the coalition is formed, it appears increasingly unlikely it will win international backing. The new government's political program falls short of a key condition by the international community, explicit recognition of Israel. Instead, it contains a vague promise to "respect" international agreements, at best implying recognition.

Hamas is considered a terror group by the U.S., the EU and Israel, and the Hamas-led governemnt was targeted by a crippling international aid boycott.

Abbas aides said Thursday that U.S. officials made it clear that Washington would boycott the emerging Palestinian government, including independent and Fatah Cabinet ministers. Abbas, elected separately, would not be included in such a boycott, the aides said.

Speaking to reporters in Washington on Thursday, Secretary of State Condoleezza Rice did not say the U.S. would boycott the new government, though she said she has seen no evidence that it intends to meet the international demands. Peace efforts were "obviously more complicated because of the uncertainties surrounding the national unity government," she said.

However, Rice said, she would reserve judgment until the government is formed. "Talking about recognizing or not recognizing the government" is premature, Rice said. "There isn't one yet. When there is one, the United States will make a determination."

Rice spoke ahead of a trip to the Middle East for a three-way summit with Abbas and Israeli Prime Minister Ehud Olmert on Monday.

Initially billed as a step toward resuming peace talks, frozen for more than six years, the summit will now likely be overshadowed by the disagreements over the Palestinian government.

In an interview on Palestinian TV late Thursday, Abbas told his people the boycott would not be lifted right away, but "we will fight and struggle, and we hope this can be accomplished soon, though there are still obstacles."

Abbas also said the letter appointing Haniyeh to form the government implicitly backs peace talks with Israel, which he would lead.

The international demands have put Abbas in a bind. Had he pulled out of the deal with Hamas, he could have been branded a traitor by his people, become increasingly ineffective and triggered more factional fighting. Since May, more than 130 Palestinians have been killed in Fatah-Hamas clashes.

In moving forward with the new partnership, however, Abbas will likely deepen the Palestinians' isolation.

Abbas will meet on Saturday with David Welch, a senior U.S. State Department official, and on Sunday with Rice, in part to try to persuade them to change their position, the Abbas aides said.

The Palestinians also hope Saudi Arabia, a U.S. ally, will help. Saudi Arabia brokered the Mecca power-sharing deal that formed the basis for the Hamas-Fatah coalition talks.

Fatah spokesman Abdel Hakim Awad said Saudi Arabia would be the guarantor of the agreement "because of the influence it has in the international, Arab and Islamic arenas."