RAMALLAH, West Bank - Palestinian leader Mahmoud Abbas pledged Saturday to track down and punish militants responsible for a suicide bombing that killed four Israelis at a Tel Aviv nightclub. Palestinian security officials pointed to the Lebanese guerrilla group Hezbollah as the apparent mastermind.

Israel and the United States said Abbas has to act quickly and forcefully - despite his long-standing reluctance to confront militants - if he wants to rescue a fragile Mideast truce.

Abbas' new Cabinet and security chiefs met Saturday to discuss a possible response. Abbas condemned the attack as "sabotage" and said he believed a "third party" was responsible, though he did not mention Hezbollah. He said he was exchanging information with Israel, the United States and Europe and hoped the attack would not derail efforts to resume peace talks.

The bomber was identified as Abdullah Badran, 21, a university student who according to his parents was a devout Muslim but had no history of militant activity.

The three main militant groups - Hamas, Islamic Jihad and the Al Aqsa Martyrs' Brigades - denied involvement, and none hung the customary posters of congratulations at the bomber's home.

Palestinian security officials said they were investigating whether Badrawn was recruited by local militants from Al Aqsa, which has ties to Abbas' ruling Fatah movement, at the behest of Hezbollah. The Lebanese group has stepped up efforts in recent weeks to disrupt the truce declared Feb. 8.

The bomber detonated a powerful bomb -radio reports said it weighed 66 pounds - around 11:30 p.m. Friday among Israelis waiting outside the seaside nightclub Stage.

Police said the guards outside the club spotted the bomber and didn't let him in. The explosion dispersed thousands of metal shards that had been packed into the bomb, cutting down people standing nearby. It ripped off the front of the nightclub, shattering windows of nearby restaurants and blackening cars.

The bodies of a young woman and the bomber lay under white plastic bags in a pool of blood and shattered glass covered the sidewalk. Three of the wounded died on their way to hospital, and 50 people were wounded, paramedics said.

Israeli Defense Minister Shaul Mofaz was to meet with army chiefs after the end of the Jewish Sabbath at sundown Saturday, but it appeared there would be no immediate Israeli retaliation and that Abbas would be given some time to act.

Israeli Cabinet minister Binyamin Ben-Eliezer said Abbas must move quickly. "This time, words are not enough. He has to combat terrorism," Ben-Eliezer, a former defense minister, told Israel Army Radio on Saturday.

Abbas pledged to track down those responsible for the attack, accusing them of trying to derail the peace process. "There is a third party that wants to sabotage this process," he said in a veiled reference to Hezbollah. "This act harms our interests, our path and our goals, and we will not hesitate for a minute to track them down, bring them to justice and punish them," he told reporters Saturday.

Israeli troops entered the village of Deir al Ghusun early Saturday and arrested two of Badran's brothers and four other village residents, including the local mosque preacher, Palestinian security officials said. The Badran family said it was informed by the army that Abdullah was the Tel Aviv bomber.

The army confirmed the arrest raid but gave no further details.

Palestinian officials and a West Bank militant leader said they believed Hezbollah had orchestrated the attack. Palestinian officials said they had been tracking communications between Hezbollah and Al Aqsa militants in the northern West Bank in recent days.

Hezbollah declined comment. "As far as we are concerned, there is no need to respond to such lies," a Hezbollah official said in Beirut.

However, Hezbollah has emerged as the biggest threat to the fragile Israeli-Palestinian truce, offering West Bank gunmen thousands of dollars to attack Israelis. The group, which is backed by Iran and Syria, has hundreds of West Bank gunmen on its payroll, according to Palestinian security officials.

Hamas, Islamic Jihad and the Al Aqsa Martyrs' Brigades, the largest Palestinian militant groups, all denied involvement, saying they were respecting the informal truce.

Since this month's Mideast summit, the two sides have stepped up security cooperation, and Israel has pledged to hand over security responsibilities in most of the West Bank to Palestinian forces.

The radical Palestinian factions are expected to hold talks with Egyptian officials next week on the cease-fire with Israel, a senior Hamas official said on condition of anonymity.