The Islamist movement, Hamas, has said Palestinians will not be bound by any decisions taken at this week's US-backed Middle East peace conference.
Hamas will not be represented at the Annapolis conference
Ismail Haniya, a leader of the group that is not attending the talks, said discussions would be "fruitless".
Some 40 countries and organisations have been invited to the conference on Tuesday in Annapolis, Maryland.
Israeli and Palestinian negotiators have been meeting in Washington to set out basic terms for the negotiations.
US President George W Bush is also holding separate talks with the Israeli Prime Minister, Ehud Olmert, and the Palestinian Authority President, Mahmoud Abbas, on Monday.
Ahead of Tuesday's conference, several Hamas leaders met at the Palestinian parliament in Gaza City to sign a document stating that Mr Abbas had no right to make concessions in any peace deal.
"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," Mr Haniya said as he entered the building.
"It will be binding only for those who sign it."
Mr Haniya was dismissed by Mr Abbas from his position of prime minister of a national unity government in June shortly after Hamas seized control of the Gaza Strip from the president's Fatah movement.
He was appointed to the role following his group's landslide victory in the January 2006 legislative election.
Hamas, which is designated a terrorist organisation by the US, EU and Israel, is not represented at Annapolis at all.
Another senior Hamas leader in Gaza, Mahmoud Zahhar, told the BBC that even if the group had been invited, it would be pointless participating because Israel was not prepared to end the occupation of Palestinian land.
"We are very proud that we are not involved in this conference which will bring for us nothing," he told the BBC World Service.
"We don't believe that this is a real peace process, because without fulfilling our basic demand it will be just as previous agreements reached and unable to be practised practically on the ground," he added.
"Abu Mazen [Mahmoud Abbas] is not representing the majority of the Palestinian people."
Palestinian officials say, however, that as chairman of the Palestine Liberation Organisation (PLO), Mr Abbas is entitled to negotiate on behalf of Palestinians. Agreements are signed between Israel and the PLO.
Earlier, US officials played down expectations of any breakthrough at the meeting the US naval academy in Annapolis, the first fully-fledged talks on Middle East peace since 2000.
President Bush's National Security Advisor, Stephen Hadley, said the conference was not a negotiation session but was designed to launch negotiations.
"If we get something, if they can agree on some things as an input to the negotiations, that would be fine," he told reporters on Sunday.
"But I think it is really no longer on the critical path to a successful conference."
After preliminary negotiations in Washington on Monday, both sides said they had made major progress towards agreeing a joint document setting out the basic terms of reference for future negotiations.
Yasser Abed Rabbo, a senior aide to President Abbas, said a document would be made public later on Monday or Tuesday. "There is a persistent American effort to have this statement," he told the Associated Press.
The Israeli foreign ministry spokesman, Mark Regev, said the two sides had made "important progress", but denied they had agreed a final draft.
Mr Abbas believes there is a real possibility of achieving a peace deal
A day after Syria confirmed it would attend, its ambassador to the UK, Sami Khiyami, said the meeting would be a chance for the Washington to restore the credibility it had lost in the Middle East.
"Annapolis constitutes a chance for them to prove that they understand the Middle East again and that they can become an honest broker," he told the BBC.
Syria agreed on Sunday to send Deputy Foreign Minister Faisal Mekdad after it received assurances that the status of the Golan Heights, which have been occupied by Israel since 1967, would be on the agenda.
Mr Khiyami said the issue had to be resolved as part of a comprehensive Middle East peace deal.
On Friday, Saudi Arabia announced that it would also attend the meeting, giving another boost to US efforts to win wide Arab support for the conference.
Iran's Supreme Leader, Ayatollah Ali Khamenei, has meanwhile warned that the conference is ''doomed to failure''.
In a speech to members of the Basij volunteer paramilitary force, Ayatollah Khamenei said the US and its allies had called the conference to help achieve their "evil aims" and to extend support to the "Zionist regime".