TEL AVIV -- A Palestinian suicide bomber blew himself up in a crowd of young people waiting for admission to a beachfront nightclub here last night, killing four Israelis, wounding about 50 others, and jeopardizing the delicate cease-fire that has prevailed in the Israeli-Palestinian conflict in recent weeks.
The blast left a horrific scene: The explosion hurled pieces of flesh into the main road along the Mediterranean Sea, and spattered cars around the area with bits of flesh and splotches of blood. Dozens of bodies lay in pools of blood and shattered glass on the sidewalk in front of the club after the 11:30 pm explosion.
A convenience store next door and a restaurant across the street were heavily damaged, as were numerous cars parked in the area.
About 20 to 30 people were waiting to get into the Stage nightclub near the promenade when the bomber set off explosives among them, killing himself and four of the bystanders, officials said. A witness said guards had spotted the man outside and did not let him in the club, preventing more casualties.
Helicopters circled overhead, searching for a second would-be attacker whom witnesses said fled when club security guards blocked the first bomber from entering.
It was the first suicide attack in Israel since a bombing in a Tel Aviv market nearly four months ago, and it was the most brazen challenge yet to the new Israeli-Palestinian peace initiative that followed the Jan. 9 election of Mahmoud Abbas as the Palestinian leader, succeeding the late Yasser Arafat.
Claims of responsibility for the attack initially came from both Islamic Jihad and Al Aqsa Martyrs' Brigades, according to local radio reports, but early today spokesmen for various factions of those Palestinian organizations were denying any involvement and condemning the attack.
Israeli officials said attempts to prevent a resumption of the Middle East peace process were expected, and suggested that military operations against Islamic militants -- suspended as part of recent efforts by the Israeli and Palestinian prime ministers to calm the conflict -- would resume if the Palestinian Authority did not stop the militant groups from attacking Israelis.
Ra'anan Gissin, an adviser to Prime Minister Ariel Sharon of Israel, said the blast proved that it would not be possible for Abbas to negotiate peace without disarming and dismantling Palestinian militant organizations.
''The concept that you can reach an agreement with a terrorist group has collapsed tonight," Gissin said. ''There will always be some who continue to launch attacks. You don't make agreements with them -- you fight them. Otherwise, there can be no progress on the road to peace."
Palestinian leaders acknowledged that the attack could complicate efforts to restart the peace process, and vowed to act.
In a statement issued early today, Abbas said, ''The Palestinian Authority will not stand silent in the face of this act of sabotage. We will follow and track down those responsible and they will be punished accordingly.
''What happened tonight was an act of sabotage toward the peace process and an attempt to ruin the efforts to establish a state of calm."
In Washington, Secretary of State Condoleezza Rice, who visited Israel and the West Bank two weeks ago to demonstrate US support for the renewed peace process, called on the new Palestinian leadership to go after those who carried out the bombing.
''Terrorist attacks, such as today's bombing in Tel Aviv, not only kill innocent civilians, but also undermine the aspirations and hopes of the Palestinian people," Rice said in a statement. ''We understand that the Palestinian leadership has condemned the attack. We now must see actions that send a clear message that terror will not be tolerated."
Gideon Ezra, the Israeli public security minister, said at the scene that ''it is better to fight our enemies than our brothers" -- an allusion to the conflict among Israelis over the looming evacuation of Jewish settlements in Gaza and the northernmost West Bank. He said terrorist targets ''must be dealt with" and that if the Palestinian Authority would not stop militant extremists, the Israel Defense Forces would.
Gissin said that Sharon consulted with the minister of defense and the heads of Israel's security agencies after the blast ''to consider steps Israel will take." He stressed that the agreement reached between Sharon and Abbas at their recent summit conference was that quiet on one side would be met with quiet on the other, and that in the absence of quiet ''we will do what we must to protect our citizens."
An official of the militant Al Aqsa Martyrs' Brigades, who spoke on condition that he not be identified, strongly condemned the attack and denied that the group was involved in it.
''We are committed to . . . the calmness we have reached with Mahmoud Abbas," he said. ''This attack hurts the national interests of the Palestinian people."
A spokesman for Palestinian militants being held in an Israeli prison in Beersheva told the Arabic satellite channel Al-Jazeera that the attack was committed by ''regional forces which want to sabotage the peace process" -- an apparent reference to the Iran-backed Hezbollah organization in Lebanon.
Hezbollah denied any involvement in the attack, which is sure to intensify pressure on Abbas to deal with armed organizations that are outside the Palestinian Authority's control.
The suicide bombing was the first aimed at Israelis since Jan. 19, when a bomber killed an Israeli security agent in the Gaza Strip, and the first in Israel since Nov. 1, when a suicide bomber killed three Israelis in Tel Aviv.