In the West Bank city of Hebron, some in a crowd of several thousand raised green Hamas flags, while in the city of Ramallah, senior figures of Hamas and Islamic Jihad, two militant groups normally opposed to Abbas, addressed the crowd.
"It's the right step in the right direction," Nasser al-Shaer, a former deputy prime minister from Hamas, said of the U.N. bid.
The Palestinians chose the "International Day of Solidarity with the Palestinian People" for the vote. Before it takes place, there will be a morning of speeches by supporters focusing on the rights of the Palestinians. Abbas is scheduled to speak at that meeting, and again in the afternoon when he will present the case for Palestinian statehood in the General Assembly.
U.S. Secretary of State Hillary Clinton warned Wednesday that the U.N. vote will not fulfill the goal of independent Palestinian and Israeli states living side by side in peace, which the U.S. strongly supports because that requires direct negotiations.
"We need an environment conducive to that," she told reporters in Washington. "And we've urged both parties to refrain from actions that might in any way make a return to meaningful negotiations that focus on getting to a resolution more difficult."
The U.S. Congress has threatened financial sanctions if the Palestinians improve their status at the United Nations.
Ahead of the vote, Republican Sen. Orrin Hatch filed an amendment to a defense bill Wednesday that would eliminate funding for the United Nations if the General Assembly changes Palestine's status.
Israeli government spokesman Mark Regev said that by going to the U.N., the Palestinians violate "both the spirit and the word of signed agreements to solve issues through negotiations," which broke down four years ago.
But Israeli officials appeared to back away from threats of drastic measures if the Palestinians get U.N. approval, with officials suggesting the government would take steps only if the Palestinians use their new status to act against Israel.
Regev, meanwhile, affirmed that Israel is willing to resume talks without preconditions.
U.N. diplomats said they will be listening closely to Abbas' speech to the General Assembly on Thursday afternoon before the vote to see if he makes an offer of fresh negotiations with no strings, which could lead to new talks. The Palestinians have been demanding a freeze on Israeli settlements as a precondition.
As a sign of the importance Israel attaches to the vote, Israeli Foreign Minister Avigdor Lieberman flew to New York and was scheduled to meet Secretary-General Ban Ki-moon before the vote.
Unlike the Security Council, there are no vetoes in the General Assembly and the resolution to raise the Palestinian status from an observer to a nonmember observer state only requires a majority vote for approval. To date, 132 countries — over two-thirds of the U.N. member states — have recognized the state of Palestine.
The Palestinians have been courting Western nations, especially the Europeans, seen as critical to enhancing their international standing. A number have announced they will vote "yes" including France, Italy, Spain, Norway, Denmark and Switzerland. Those opposed or abstaining include the U.S., Israel, Germany, Canada, the Netherlands and Australia.
The Palestinians turned to the General Assembly after the United States announced it would veto their bid last fall for full U.N. membership until there is a peace deal with Israel.
Following last year's move by the Palestinians to join the U.N. cultural agency UNESCO, the U.S. withheld funds from the organization, which amount to 22 percent of its budget. The U.S. also withheld money from the Palestinians.
Associated Press writers Amy Teibel in Jerusalem and Karin Laub in Ramallah, West Bank, contributed to this story.
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