A Palestinian suicide attack has shattered several weeks of calm, putting an Israeli-Palestinian ceasefire to its first big test.
The bomber killed four Israelis and injured about 50 people outside a nightclub in Tel Aviv, once again bringing scenes of death and chaos to Israel's streets.
All sides appear to want to protect the truce
But most parties seemed to be trying to protect the truce agreed by Israeli Prime Minister Ariel Sharon and Palestinian Authority President Mahmoud Abbas at a recent summit in Egypt.
Overnight, the Israeli army raided a West Bank village. Palestinians say five people were arrested, including the brothers of the alleged bomber.
However, Israeli officials suggested there were no plans for a large-scale military operation.
"The Israeli response will be punctual and will be concerned with the elements directly responsible for carrying out the attack," Israeli army radio quoted a senior defence official as saying.
But Israel is pressing for tougher action from Mr Abbas, declaring that his strategy of negotiating with the Palestinian armed groups is not good enough.
The main Palestinian factions have not officially signed up to the ceasefire. But they have been observing an informal truce and their leaderships in the occupied territories denied any link to the attack.
The Palestinian bomber gave no warning, his mother said
However, reports quoted some Islamic Jihad officials claiming responsibility for the bombing.
That could suggest a split in the movement between its inside leadership, based in Gaza, and its outside leadership based in Syria, which is said to have more influence over Jihad cells in the West Bank.
Earlier in the day, Palestinian security officials said the bomber might have been recruited by Hezbollah, the Lebanese Islamic movement that has long been accused of funding militant cells in the West Bank.
Hezbollah "unequivocally" denied the charge, calling it "a campaign of incitement led by the Hebrew state". Israel has been trying to convince the European Union to label the movement a terrorist group.
Mr Abbas said an unnamed "third party" was behind the bombing, possibly referring to Hezbollah.
On the other hand, it is convenient, and not unusual, for Palestinian officials to blame outside forces for Palestinian attacks - Yasser Arafat did it often.
Whoever was behind the attack, it is clear the Palestinian-Israeli ceasefire is fragile.
Much depends on whether this is an isolated incident or a concerted attempt to sabotage Mr Abbas' strategy of ending violence and renewing political negotiations.