Israeli forces have launched major raids into several areas of the Gaza Strip, killing five Palestinians. About 20 Palestinians were arrested in the military operation.

In a series of incursions into Palestinian-ruled areas of the Gaza Strip, Israeli troops, backed by tanks and armored personnel carriers, raided communities searching for militants and weapons.

The army says the raids on Deir al-Balah, Beit Lahia, and Beit Hanoun were in response to the firing of a new type of rocket earlier this week from Gaza into Israel.

The raids triggered sporadic gunfights. Three Palestinian policemen were killed in Deir al-Balah, while another policeman and a civilian were killed in Beit Hanoun.

The Israeli army later pulled out of two towns, but set up what appeared to be a makeshift military camp in Beit Hanoun.

An Israeli army spokeswoman says Beit Hanoun is a stronghold of the militant Hamas movement, and mortars have been fired from the town at Jewish settlements in Gaza.

Israeli cabinet minister Ephraim Sneh says soldiers could remain in Palestinian-controlled areas in Gaza for days, until rocket factories are found. He predicted the military would carry out more large-scale raids if rocket fire continues.

Sunday, militants launched Qassam-Two rockets from Gaza into Israel, causing no casualties, but alarming Israeli security officials because such weapons can reach population centers.

The Palestinian public security chief in Gaza, Abdel-Razek al-Majaydeh says "the reoccupation of the northern Gaza Strip sabotages Palestinian, international, and Arab efforts to restore calm." He says Israeli leaders will not be able to "achieve security and peace with tanks and helicopters."

On the diplomatic front, British Foreign Secretary Jack Straw arrived in the region and held meetings with top Israeli and Palestinian officials.

Mr. Straw told journalists in Jerusalem that it is impossible to revive the peace process while the violence is raging. "The first steps which have to be taken are to make the lives of the people of Israel much more secure and that means clamping down on the terrorism, which comes from the occupied territories," he said. "We recognize the overwhelming need for peace in the whole of this region. We also recognize that alongside a secure state of Israel, within borders which guarantee its peace, there is an overwhelming case for a viable state of Palestine."

Mr. Straw says Britain feels the best way to calm the situation is to follow the steps outlined in a plan by an international commission. The plan calls for an immediate cease-fire, a cooling off period, a series of confidence-building measures and a return to peace negotiations.