Palestinian Authority President Mahmoud Abbas sought to reinvigorate his Fatah movement Tuesday, launching the party's first congress in 20 years -- and its first ever in the West Bank. More than 2,000 delegates from around the world have gathered here to choose a new party platform and hold elections for Fatah institutions.

"Although peace is our choice, we reserve the right to resistance, legitimate under international law," Abbas told the delegates in an animated two-hour speech. The Palestinian leader made it clear that by "resistance," he meant nonviolent protests rather than armed confrontation, praising peaceful weekly demonstrations against a controversial barrier Israel is building in and around the West Bank.

Abbas also said that Palestinians remain committed to the goal of establishing an independent state in the West Bank and the Gaza Strip, with Jerusalem as its capital. "We are on our land, and we are not going anywhere," he said to applause.

Israel permitted delegates from throughout the Arab world, including Lebanon and Syria, to attend the conference. However, Hamas refused to allow more than 300 Fatah delegates from Gaza to leave the coastal enclave, underlining the persistent tensions between the Islamist movement, which seized control of Gaza in 2007, and Fatah, which controls the West Bank.

"I hope we will see a new organization, a new party and a new political language after this conference," said Nabil Amr, a former Palestinian cabinet minister and an outspoken critic of Abbas's predecessor, Yasser Arafat. "Mahmoud Abbas is showing he is an active and effective leader, and the Palestinian people support him."

Abbas faced some criticism from a group known as the "young guard," men in their 40s who led the first Palestinian intifada, or uprising, against Israel in the late 1980s and whose jailed leader, Marwan Barghouti, is widely mentioned as the only possible alternative to Abbas.

"We need a new Fatah that is free from corruption," said Tayseer Nasrallah, a young guard delegate from Nablus, West Bank, who spent five years in an Israeli jail and was later deported to Lebanon. "Abbas spoke for too long, but at least he criticized the movement and the mistakes we've made in the past 20 years."

Stronger criticism came from Gaza, where Hamas official Ayman Taha told the Reuters news agency that Abbas's speech reflected "a sick mentality representing a narrow factional vision."

Tensions between Hamas and Fatah have simmered since the 2006 elections in which Hamas trounced Fatah. After Hamas took over Gaza, Israel imposed a blockade, and recent polls show Hamas losing strength there while Fatah remains dominant in the West Bank.

"Hamas committed a very serious mistake preventing our members from Gaza from coming here," said Nabil Shaath, a senior Fatah official and former foreign minister. "It destroyed a lot of goodwill for Hamas in Palestinian public opinion."

Israeli officials, meanwhile, say they would like to strengthen Fatah as a counterweight to Hamas, which denies Israel's right to exist.

The Fatah conference opened amid signs that the Obama administration is planning a new push for the resumption of peace talks. A spokesman for Israeli Defense Minister Ehud Barak said Tuesday that Barak told a parliamentary committee that the United States will present a new peace plan within weeks and that, in his view, "Israel should accept it."

Israeli news media say the plan is based on a 2002 Saudi proposal calling for normalized ties between Israel and more than 50 Arab states in exchange for an independent Palestinian state in the West Bank, Gaza and East Jerusalem.

In his speech in Bethlehem, Abbas said a complete freeze on the expansion of Jewish settlements in the West Bank is a precondition for resuming talks with Israel.

Some delegates were elated to be attending such a conference at all, including Mahmoud al-Assadi. Assadi was born in Lebanon in 1960 to Palestinians who fled their village near Acre in 1948. The area later became part of Israel. He rose in Fatah's ranks to become consul general in the Palestinian Embassy in Beirut. Tuesday marked his first visit to the West Bank.

"It's very emotional and almost mystical," he said during a break in proceedings. "For so long, Yasser Arafat spoke about the dream of a Palestinian state. Now Mahmoud Abbas is following in his footsteps to achieve it."