Hours before the start of a U.S.-hosted Middle East peace conference, Gaza's Hamas rulers stepped up their attacks on Palestinian Authority Chairman Mahmoud Abbas, calling him a traitor and saying they would reject any decisions that come out of the international gathering.

"The Land of Palestine ... is purely owned by the Palestinians," senior Hamas official Mahmoud Zahar said in a speech. "No person, group, government or generation has the right to give up one inch of it."

"Anyone who stands in the face of resistance or fights it or cooperates with the occupation against it is a traitor," he added. He spoke at a conference, held in Gaza City, attended by some 2,000 activists from local militant groups opposed to the U.S. conference.

Hamas and other militant groups have been holding a series of protests this week against the U.S. peace conference, underscoring the challenges Abbas faces at home as he tries to make peace with Israel.

Hamas violently seized control of Gaza from Abbas' forces in June, leaving him in charge of a pro-Western government based in the West Bank. Abbas' lack of control over Gaza has raised questions about his ability to carry out any future peace deal.

While moving to bolster Abbas, Israel has stepped up pressure on Hamas since the Gaza takeover, carrying out numerous airstrikes and ground incursions to halt Palestinian militant attacks. On Monday, the Israel Defense Forces killed at least four Hamas militants in two separate incidents in the northern Gaza Strip.

Hamas' criticism of Abbas has grown increasingly heated - and personal - ahead of the Mideast conference. Ismail Haniyeh, prime minister of Gaza's Hamas government, was among a series of Hamas leaders to sign a document Monday stating that Abbas has no right to make concessions in peace talks.

"The people believe that this conference is fruitless and that any recommendations or commitments made in the conference that harm our rights will not be binding for our people," Haniyeh said. "It will be binding only for those who sign it."

A senior member of the militant movement Islamic Jihad, Mohammed al-Hindi, said at the gathering "we believe that with patience, we will change the rules of the game." ,

"Our jihad and sacrifice will bring us the great victory we are looking for," he added.

Al-Hindi said that the peace talks will promote "a false illusion of a Palestinian state" and that "such a state would be divided and surrounded by Israel and its task would be striking the resistance and protecting Israel."

"This conference is to announce the rise of the Palestinian people, who will not beg for their rights" from Bush, U.S. Secretary of State Condoleezza Rice, Prime Minister Ehud Olmert and Foreign Minister Tzipi Livni, al-Hindi declared.

The U.S. summit was getting under way Monday in Washington, with U.S. President George W. Bush inviting the Israeli and Palestinian leaders to separate meetings at the White House before an opening dinner later in the day. The centerpiece of the gathering will be an all-day session Tuesday in Annapolis, Maryland, to be attended by representatives of 16 Arab countries, including Saudi Arabia and Syria.