More than ten Palestinian militants belonging to Palestinian leader Mr Yasser Arafat's Fatah movement and the radical Islamic movements Hamas and Islamic Jihad were arrested by the Israeli army today, Palestinian security sources said.
Houses were also searched in the northern West Bank town of Jenin from where several suicide bombers have originated.
Meanwhile, dozens of men aged 15 to 50 were rounded up in Jenin's refugee camp, a hotbed of Islamic Jihad militants, and interrogated in a UN school there. The army also proceeded to search houses in the camp, according to the same sources.
The camp in April bore the brunt of the massive six-week Israeli offensive in the West Bank launched following earlier suicide attacks.
Israeli infantry units backed by armored personnel carriers and tanks under cover of helicopter gunships had entered Jenin and its camp earlier today.
The moves came hours after Israel decided to take military action in retaliation for a Palestinian suicide attack on a Jerusalem bus yesterday which killed 19 people plus the bomber.
The Palestinian sources said the Israeli army had towed at least seven caravans into the refugee camp, suggesting it was going to stay for some time.
Israel said after a meeting of the mini-cabinet chaired by Prime Minister Mr Ariel Sharon it would partially reoccupy Palestinian territory.
Officials said Israel's military actions would be on a larger scale than recent raids, which have regularly involved Jenin, among other towns, but not of the massive scope of the operation between March 29th and May 10th.
AFP