Two women died on the spot and two others later succumbed to wounds sustained in the blast.
Early on Wednesday, Israeli troops shot and killed a Palestinian policeman during a raid on a West Bank town in what the army called a retaliation for a bombing that dealt a blow to a five-month-old ceasefire.
The occupation army said the policemen had fired on troops hunting down members of resistance group Islamic Jihad.
Troops fired at a Palestinian security post, killing a policeman and wounding another in what witnesses called an unprovoked attack.
Military sources said the army shot back after two soldiers were wounded by fire from Palestinian armed men.
Curfew and arrests
Troops also declared a curfew on Tulkarim, in effect taking back control of an area that Israel handed back to Palestinians in March under the terms of an unofficial ceasefire declared in February.
Brigadier-General Yair Golan, commander of the West Bank division of the Israeli army, said the operation was open-ended.
A Palestinian policemen was shot
and killed by Israeli troops
Witnesses said about 20 military vehicles were involved in the raid.
Troops also arrested five people suspected of being members of Islamic Jihad in the Tulkarim area of the northern West Bank, just hours after the Palestinian resistance group claimed responsibility for Tuesday's attack where a bomber blew himself up at a shopping centre in Netanya, 12km from the West Bank.
Four Israeli women were killed and dozens more people wounded.
"Five Islamic Jihad terrorists have been arrested during IDF (Israel Defence Forces) activity in the Tulkarim area during the
night and early this morning," an army spokeswoman said.
Islamic Jihad claim
Al-Quds Brigades, linked to the Palestinian resistance group Islamic Jihad, claimed responsibility for Tuesday's attack, reported Aljazeera.
Israeli police and Palestinian security identified the bomber as Ahmad Sami Abu Khalil, an 18-year-old member of Islamic Jihad.
The Israeli military raided the
city and imposed a curfew
Aljazeera correspondent Walid al-Umari said the bomber came from Atil town, north of Tulkarim.
In a statement after the attack, Islamic Jihad said it remained committed to the ceasefire agreed to in February but reserved the right to retaliate for Israeli violations, such as arrests of the resistance group's members.
Military sources said the Israeli army was still in Tulkarim, but
were unable to confirm whether the five detainees were wanted directly for Tuesday's attack, saying only that all of them were active members of Islamic Jihad.
Israeli Prime Minister Ariel Sharon on Wednesday ordered his security forces to target the leaders of Islamic Jihad in the wake of Tuesday's blast.
Speaking to a group of new immigrants at Ben Gurion International Airport, Sharon promised swift action.
"Yesterday I ordered the security forces to increase our actions and hit the leadership of the Islamic Jihad. We will not stop until they stop the terrorist murders," he said.
The army also sealed off the occupied West Bank and Gaza
Strip early on Wednesday.
The ban on Palestinians entering Israel
will mean that thousands of Palestinians who have work permits will not be allowed to enter Israel for work.
The military said the ban, a routine security measure after such an attack and approved by the government, would be in effect until further notice.Will pullout continue?
Meanwhile, James Wolfensohn, the Middle East quartet's special envoy for the Gaza Strip pullout, expressed hope
on Wednesday that Tuesday's attack would not affect the withdrawal.
"I would hope that it does not because that's just what the
"My central point is that not only was this a terrible attack on the Israeli people but also an attack on the Palestinian people because it makes the chance of a resolution of the conflict, in a way that the Palestinian people are striving for peace and hope, much more difficult"
James Wolfensohn, special envoy of Middle East quartet
terrorists want," the former World Bank chief said.
"I think there's a real interest for both peoples to bring about
a peaceful resolution," he told Israeli public radio.
Israel is due to withdraw all its troops and between 8000 and 9000 settlers from Gaza in an operation beginning next month.
"My central point is that not only was this a terrible attack on the Israeli people but also an attack on the Palestinian people because it makes the chance of a resolution of the conflict, in a way that the Palestinian people are striving for peace and hope, much more difficult," Wolfensohn said.