Israeli leader Ariel Sharon has ordered his forces to shatter a Palestinian militant group, after a suicide bomb killed four Israelis.
Israeli soldiers take up positions in Tulkarm
Islamic Jihad said it was behind Tuesday's bomb in the town of Netanya that upset a fragile four-month truce.
Earlier on Wednesday, Israeli forces entered Tulkarm in the West Bank, effectively retaking a town ceded to the Palestinians in March.
Troops arrest five suspected militants and shot a Palestinian policeman dead.
Separately, Israeli forces also blocked entry for non-residents to Gaza Strip settlements ahead of a planned pullout due to begin in August.
Israeli media reports said it was to forestall Israeli settler protests against the withdrawal. Right-wing Jews responded by blocking a highway between Jerusalem and Tel Aviv, chanting "Jews don't expel Jews".
'Transfer on hold'
"I ordered the defence establishment to increase our activity and to do as much harm as possible to the leadership of the Islamic Jihad terror organisation," Mr Sharon said in a speech near Tel Aviv.
"We will not leave them alone until they stop these murderous acts."
Correspondents say the move is expected to involve an increase in targeted killings of Palestinian militants - a policy that has been suspended since an unofficial ceasefire was agreed in February.
Israeli forces have sealed off the West Bank and the transfer of the towns of Ramallah, Bethlehem and Qalqilya to the Palestinians - a key pledge in a peace deal agreed last February - has been put on hold, an Israeli official said.
Pressure on Abbas
Five people - including the bomber - died in Tuesday's blast outside a shopping centre in Netanya.
Israeli intelligence officials say the bombing was an attempt by Islamic Jihad to derail Mr Sharon's plans to disengage from Gaza, Israeli daily Haaretz reports.
They said the group - which was also implicated in a bombing outside a Tel Aviv nightclub earlier this year - is trying to drag the Hamas militant organisation into disrupting the pullout, according to the paper.
Israeli Defence Minister Shaul Mofaz has reportedly ordered the Palestinian leader, Mahmoud Abbas, to crack down on the militants, warning him Israel will act where he fails to do so.
Mr Abbas has condemned the bombing, describing it as the work of "traitors" who were "working against the Palestinian interest".