Hamas on Saturday marked its 20th anniversary by vowing to continue the "jihad" against Israel and never recognize its right to exist. Tens of thousands of Palestinians participated in a main rally organized by Hamas in the center of Gaza City in what was seen as one of the movement's biggest shows of force. Shouting, "We won't recognize Israel," the Hamas supporters burned Israeli flags and chanted slogans against the US. The rally was held in the same square where thousands of Fatah supporters attended a memorial for Yasser Arafat last month. Hamas officials estimated that nearly 250,000 Palestinians participated in the rally as opposed to less than 50,000 who showed up for the Arafat event. Fatah representatives claimed that the Hamas rally was a "failure" because of the "small" number of participants. "This is Hamas's poorest performance since 1997," said Fatah spokesman Jamal Nazzal. "Hamas threatened to cut off the salary [of] and beat any activist who does not bring his family members to the rally. Despite that, they were unable to fill the square, and there were many empty chairs." The rally came amid increased tensions between Hamas and Fatah following the arrest of two senior Fatah figures in the Gaza Strip. One of them, Omar Ghul, is a special adviser to PA Prime Minister Salaam Fayad. He was arrested shortly after returning to the Gaza Strip from Ramallah to participate in the funeral of his mother-in-law. Hamas said Ghul was arrested after he entered the Gaza Strip through the Erez border crossing in disguise. The second man who was arrested was Ismail Abu Naja, a former deputy speaker of the Palestinian parliament. Abu Naja was arrested after holding a press conference in Gaza City at which he accused Hamas of killing three Palestinians during a funeral on Friday. The three were killed by an explosive device that apparently went off accidentally during the funeral of Islamic Jihad members who had been killed a day earlier in an Israeli attack. Abu Naja and many Fatah officials in Ramallah were quick to blame Hamas for the explosion, saying it was a deliberate attack on civilians. The Palestinian security forces in the West Bank banned Hamas celebrations by deploying hundreds of policemen in main cities and removing all Hamas-affiliated graffiti and flags. Several Hamas figures were summoned to the Palestinian security forces and warned not to hold any events marking the Hamas anniversary. Hamas said 26 of its followers were arrested over the weekend in the West Bank by Fatah-controlled forces. "The IDF's withdrawal from Gaza will be nothing like its invasion, the Strip will become a graveyard for its troops," Hamas legislator Mushir al-Masri warned Saturday in his chilling opening address at the Gaza rally. "Jews... we have already dug your graves," exclaimed Masri. Hamas Prime Minister Ismail Haniyeh said his movement would pursue the "resistance" as the only option to "liberate Palestine." He said the large turnout was an indication of the increased number of Palestinians who believed in Hamas and didn't accept Israel's right to exist. Haniyeh pointed out that those who believe in the "resistance" and the concept that "Islam is the solution" have scored a number of victories over the past few years: the Israeli withdrawal from southern Lebanon in 2000, the Israeli withdrawal from the Gaza Strip in 2005, the abduction of IDF Cpl. Gilad Schalit in 2006 and the beginning of the "defeat" of the Americans in Iraq and Afghanistan this year. Haniyeh said that "Whoever insists on not recognizing Israel, clings to Allah and doesn't surrender in the face of the Israeli and US blockade, his popularity grows despite American hostility." "As long as the Israeli oppression grows, so will his popularity." Top Hamas official Osama al-Mazini told the crowd that Israel was afraid to invade the Gaza Strip to stop the rocket and mortar attacks on its cities. "Had they not been afraid of your resistance, the Israelis would have invaded the Gaza Strip a long time ago," he said. "But the Israeli enemy are cowards and the only language they understand is the language of force." He said Hamas had chosen jihad (holy war) as its strategy and would not change its policy under any circumstances. Referring to the case of Gilad Schalit, the Hamas official said the soldier would "never see the light until all Palestinian prisoners are released from Israeli jails." Mazini said Hamas would never recognize Israel or give up Palestinian rights, including the "right of return" for Palestinian refugees. The Hamas official launched a scathing attack on Palestinian Authority President Mahmoud Abbas and his Fatah faction, accusing them of "selling themselves to the Americans and agreeing to serve as guards for Israeli occupation." However, he reiterated Hamas's readiness to engage in dialogue with Fatah to solve the current crisis. Hamas, he added, "never thought of opening fire at Fatah." He said that, in any case, Hamas would not allow Fatah to bring anarchy and lawlessness back to the Gaza Strip. Syria-based Hamas leader Khaled Mashaal threatened during a televised speech to launch a "third and fourth intifada" against Israel. He added that his movement had a lot of patience "despite the ongoing conspiracies and the blockade against the Gaza Strip." He, too, said one of Hamas's biggest achievements was to "expel" Israel from the Gaza Strip in 2005. Mashaal claimed that Israel was using the recent peace conference in Annapolis as a cover for launching a "massive aggression" against the Palestinians in the Gaza Strip. He also claimed that the US-sponsored conference had given Abbas a green light to "dismantle resistance groups in the West Bank."