Talks in Annapolis, Maryland, began on Tuesday, and involve Arab states and Israel, Mideast mediators, and international organizations. The main goal of the conference is to restart talks on Palestinian statehood.
The rally, which Hamas said drew some 250,000 protesters, marked a high point in a series of public gatherings intended to demonstrate Palestinian opposition to the Annapolis conference. Other estimates by journalists put the crowd at 100,000. One person was reported to have been killed during the rally.
On Gaza's central square, the crowd chanted slogans: "Down with the devils who have gathered in America," "Palestine and Jerusalem are not for sale," "We will never recognize Israel," and "Our refugees must return home."
The rally was attended by all of the Islamist group's leaders, including Hamas Prime Minister Ismail Haniyeh, acting speaker of the PNA parliament Ahmad Bahar, as well as leaders of the Islamic Jihad and other armed organizations.
Hamas seized control of the Gaza in June after a series of clashes with Palestinian President Mahmoud Abbas' Fatah movement.
A Fatah leader said in Cairo that the real battle for peace in the Middle East would start after the Annapolis conference.
"The Annapolis conference will not bring an immediate resolution to the Arab-Israeli conflict," Muhammed Dahlan said.
Israeli Prime Minister Ehud Olmert said earlier on Tuesday that the Mideast peace conference would help Israel establish diplomatic relations with Arab countries.
Egypt and Jordan are currently the only Arab nations that have diplomatic relations with Tel Aviv.
Israel's Haaretz daily newspaper reported that during his meeting on Tuesday with UN Secretary General Ban Ki-moon, Ehud Olmert said he did not expect an immediate improvement in Israeli-Arab relations, but hoped for goodwill gestures following the conference, such as the opening of consular offices in Israel.
The Annapolis conference kicked off with a meeting between U.S. President George W. Bush, Palestinian President Mahmoud Abbas and the Israeli premier. The three leaders will depart after addressing the conference, and meetings will continue at a foreign ministerial level, to be presided over by U.S. Secretary of State Condoleezza Rice.
Sixteen Arab nations, including Saudi Arabia, agreed to send their foreign ministers to the conference following major diplomatic efforts by Washington.
The Palestinians and the Israelis have so far failed to coordinate a final document for the conference. The Palestinian leadership has insisted on specific agreements, while Tel Aviv has rejected binding commitments.
Arab states have pledged to improve relations with Israel when an independent Palestinian state is formed, with its capital in East Jerusalem, and Palestinian refugees are brought home. They are also seeking an Israeli withdrawal from Palestinian lands occupied in the 1967 Israel-Arab War, as well as from Syria's Golan Heights.
Haaretz quoted Olmert as saying in the U.S. that Abbas must bring radical Islamists in the West Bank and the Gaza Strip under control as a condition for further peace talks.
