Israeli tanks and troops have moved into the West Bank town of Hebron, killing four Palestinian policemen in the latest incursion into areas under the control of the Palestinian Authority.

An Israeli military statement said a "large number" of suspected militants were arrested in Hebron and that soldiers also discovered an explosives factory there. Residents said Israeli troops declared a curfew in the city.

Hebron is the seventh Palestinian city to be taken over in the past week since a series of Palestinian attacks that killed more than 30 Israelis.

The action in Hebron came just hours after President Bush laid out his ideas about how peace in the Middle East might be achieved. In it, he called for a new Palestinian leadership that is, as he put it, "not compromised by terror." He did not mention Yasser Arafat by name.

Israel welcomed the speech, but Palestinians objected to it, even though it called for the eventual creation of a Palestinian state. Their chief objection was the call for a change in their leadership.

Meanwhile, an Israeli missile attack in the Gaza Strip on Monday killed six Palestinians, including four members of the militant group Hamas. One of those killed was Yasser Rezik, who was wanted by Israel for allegedly killing Israelis in the past and planning future suicide attacks.

Israeli Prime Minister Ariel Sharon said the helicopter attack was the first Israeli strike in a new massive campaign against Hamas.

He told members of his Likud party on Monday that the attacks will be targeting what he called terrorists, their strongholds, and their commanders. He said the military operations will put Israeli troops in Palestinian towns for an extended, unlimited period.

Israeli tanks also moved into Ramallah on Monday, surrounding the heavily-damaged headquarters of Palestinian leader Yasser Arafat.