Israel's defense minister said the raids were aimed at pressuring Hamas to halt rocket attacks from Gaza that have terrorized an Israeli border town. Israel also launched air strikes in Gaza targeting money changers whom the army said transferred funds from Iran, Syria and Lebanon To Hamas for terrorist activities.
Meanwhile, the latest effort to restore an Israeli-Palestinian cease-fire in the Gaza Strip failed when Hamas rejected a call by moderate Palestinian President Mahmoud Abbas to halt the rocket attacks on Israel. Hamas said there would be no truce unless it includes the West Bank in addition to Gaza. Israel refused, saying it West Bank raids are necessary to prevent suicide bombings.
Thursday's Israeli air strikes in Gaza hit Hamas bases in Gaza City and in central Gaza, near the town of Deir al-Balah.
At sundown Thursday, a mortar shell fired from Gaza exploded at Erez, the main crossing for people between Israel and Gaza, and Israel closed the crossing, the military said. There was considerable damage but no one was hurt.
The Israeli army said it arrested 33 Hamas leaders in its overnight sweep. The most prominent official taken in the roundup was Education Minister Nasser Shaer, considered a pragmatist in the movement.
His wife, Huda, said soldiers knocked on the door of their home in the West Bank city of Nablus and took him away. Troops also seized Shaer's computer, she said. Israel also detained Shaer for a month last year during a similar crackdown before a judge ordered his release.
Defense Minister Amir Peretz said that in the fight to neutralize Hamas, arrests were preferable to bloodshed.
"Arrests are better than shooting," he told Israeli Army Radio. "The arrest of these Hamas leaders sends a message to the military organizations that we demand that this firing (of rockets) stop."
But Hamas said the attacks would continue. "We will chase the occupation soldiers and the settlers in every inch of our occupied land, and we announce that we give free hand to our cells to strike against the enemy in every place in Palestine," according to a statement. "Palestine" is a Hamas term that includes Israel.
Abbas said the arrests were a blow to peace efforts, and a spokesman for Palestinian Prime Minister Ismail Haniyeh, of Hamas, called for the immediate release of the detainees and called on the U.N. and European Union to impose sanctions on Israel.
Hamas leaders are worried Israel may assassinate Haniyeh or Hamas chief Khalid Mashaal, who lives in Syria, reports the Jerusalem Post, quoting Palestinian Authority officials. "Hamas is taking the Israeli threats very seriously," said one.
If either man is killed by Israel, the Palestinians' response would be "very painful," Hamas legislator Salah Bardaweel told the Post.
Visiting EU foreign policy chief Javier Solana met Abbas in Gaza on Thursday and called for Palestinians and Israelis to stop the violence.
"The rockets and the Israeli response have to stop," he told reporters after the meeting.
Abbas himself condemned what he called the "absurd" rocket fire and said he was trying to persuade militant groups to stop. "They must stop so we can reach a truce with Israel," he said.
Palestinian Authority spokesman Ghazi Hamad said, "These aggressive practices show the extent of the Israeli escalation and arrogance in the Palestinian territories, and also show how dismissive the Israeli government is of all customs and international laws."