Israeli tanks backed by attack helicopters invaded a refugee camp near the Gaza-Egypt border late Wednesday, clashing with gunmen and killing four Palestinians, doctors said.

Earlier, Israeli troops rounded up hundreds of men in a sweep of the West Bank town of Tulkarem and demolished the home of a jailed Palestinian accused in a string of attacks.

In Gaza, residents said about 25 tanks and several bulldozers entered the refugee camp next to the town of Rafah. Palestinian gunmen shot at the soldiers, and an Apache helicopter fired back, killing a Palestinian. Three others died in exchanges of fire, and seven were wounded in the violence, doctors said.

The Israeli military would say only that an operation was in progress. Israel Radio reported that four Israeli soldiers were wounded when a bomb went off under a tank.

The area is the scene of daily clashes between armed Palestinians and Israeli soldiers, and Israel often sends in bulldozers to destroy buildings used by gunmen for cover.

In Nablus, Israeli troops shot and killed a leader of the militant Hamas group during a raid on his hideout early Thursday morning, the army said. Khaled Rayyan, 28, was hiding in a relative's house when soldiers broke down the door, said his wife, Salam Rayyan. Rayyan was killed when he tried to attack the troops with a pistol, his wife said.

The arrested men in Tulkarem were held in a barbed wire enclosure for several hours and then all but seven were released. Another four suspected militants, including a Hamas member accused of planning shooting attacks, were arrested elsewhere in the West Bank.

The military said that during the Tulkarem operation troops caught a wanted militant trying to slip out of the town's refugee camp disguised in women's clothing.

The military's operations came as Mahmoud Abbas, the recently named Palestinian prime minister, met with political leaders in the Gaza Strip Wednesday to discuss the formation of his new Cabinet, expected later this month.

Abbas also met in recent days with leaders of the Hamas militant group, based in Gaza. Abbas has been trying to persuade Hamas and the smaller Islamic Jihad to end, at least for a period, attacks against Israelis.

Israel has said a U.S.-backed "road map" for Palestinian statehood cannot move forward as long as attacks persist. President Bush said the road map will be formally presented as soon as Abbas and his Cabinet are officially confirmed.

Meanwhile, there were other signals of a possible thaw in Israeli-Palestinian relations, which have been devastated by 30 months of deadly violence and bitter recrimination.

Israeli security officials met for the first time in months with Palestinian security officials, according to Ribhi Arafat, a Palestinian commander. Two meetings took place last Tuesday and Thursday, in Israel near the Gaza border, he said.

Under interim peace accords, the Palestinian Authority is supposed to control about 40 percent of the West Bank, but in a series of incursions that followed suicide bomb attacks, the Israeli military has gradually retaken most of the areas, including all but one of the main Palestinian cities and towns.

A spokeswoman from the Israeli Defense Ministry would neither confirm nor deny that the security meetings took place.

Reviving security talks would be one of many steps that could help thaw icy relations between the two sides, who have been locked in 30 months of fighting. Both are under international pressure to end the violence and resume peace talks.

On Wednesday, Israeli troops arrested four men in the West Bank town of Hebron. Two allegedly belonged to Hamas, while the other two belonged to Islamic Jihad, which claimed responsibility for a suicide bombing Sunday in the coastal town of Netanya. The attack wounded dozens of Israelis.

Soldiers on Wednesday also demolished the home of Omar Abu Sneineh in Hebron, a member of the Al Aqsa Martyrs Brigade, which is linked to Yasser Arafat's Fatah party. He was jailed three months ago after being accused in bomb attacks and shootings, the army said.