Ten people have died in one of the bloodiest days of Israeli-Palestinian violence in months.
The deaths threaten to trigger a new wave of violence
Four Israelis and a Palestinian suicide bomber were killed in an attack at a bus stop near the Israeli city of Tel Aviv.
The blast occurred shortly after Israeli helicopters killed three militants and two bystanders in an attack on a car in Gaza City.
One of those killed was a commander of the radical Islamic Jihad movement.
Israeli army spokesman Jacob Dallal said the commander, Mekled Hameid, was a "ticking bomb... in the midst of planning a major attack".
Islamic Jihad vowed to retaliate for Mr Hameid's death.
"We promise the [Israeli] occupiers severe retaliation for the assassination crime... the Zionist occupation will pay dearly for the murder," the group told the Associated Press (AP) news agency.
Israel has used helicopters to track and kill dozens of militants fighting in the three-year-old Palestinian uprising known as the intifada.
Palestinian Prime Minister Ahmed Qurei condemned both attacks.
"Regretting the continuation of the cycle of assassinations,
liquidations and attacks against civilians on both sides, the prime
minister calls for a stop to this bloody circle and the conclusion
of a reciprocal cease fire," a cabinet statement said.
But following the Tel Aviv blast, Israeli Defence Minister Shaul Mofaz announced the "total closure" of the Palestinian territories, a spokesman told AFP news agency.
Israeli Health Minister Dan Naveh, while visiting the wounded, blamed Palestinian leader Yasser
Arafat for the Tel Aviv bombing.
"Before we consider a political
move, by agreement or unilateral, we must expel the terror
regime of Arafat and the gang of terrorists that comes with
him," he said.
The blast happened at around 1800 local time (1600 GMT) at Geha, a major junction outside Tel Aviv.
The bus hit in the explosion was on its way to the nearby town of Petah Tikva. Three women and a man were killed and at least 12 others were injured, several seriously.
routinely gather at the junction to seek illegal employment, according to police.
An eye-witness told Israel Radio that there were wounded people lying everywhere. He said other cars were hit by the blast.
The Popular Front for the Liberation of Palestine (PFLP) said it carried out the attack, which, it said, would be the first in a "series of retaliations".
It named the bomber as 18-year-old Said Hanani, 18, from the village
of Beit Furik, near the West Bank city of Nablus, AP reported.
The bombing is the first such attack since a bomb at a restaurant in the northern Israeli city of Haifa killed 21 people in October, though Israeli officials say they have captured more than 20 potential suicide bombers trying to enter Israel since then.
The Gaza attack is also the first of its kind for several months.
The BBC's Simon Wilson in Jerusalem says this week is proving the bloodiest in the conflict for several months.
In a separate incident in Gaza, the Israeli army said earlier it had foiled an attempted Palestinian militant attack by shooting a man dead.
An Israeli raid in Gaza on Tuesday left nine people dead.
The raid led Palestinian leaders to cancel a planned meeting with Israeli officials.
Correspondents say Thursday's violence is certain to set back even further tentative efforts at peacemaking which have been under way over the last few weeks.