Israeli forces occupied the West Bank city of Nablus early Friday in a response to an attack by Palestinian gunmen on a nearby settlement hours earlier.

Palestinians said about 50 tanks and several bulldozers moved into Nablus from three directions, meeting with no initial resistance.

Sending forces into Nablus appears to be Israel's latest action under its new policy of occupying Palestinian Authority land every time Palestinian militants attack Israelis.

The attack on the settlement of Itamar killed at least six Israelis, including a mother and three of her children, and wounded at least eight others. The gunmen burst into the victims' home and opened fire.

Israel Radio said soldiers shot and killed one of the infiltrators, and another jumped out a window. Soldiers exchanged fire with him, the report said.

The Popular Front for the Liberation of Palestine claimed responsibility, while Prime Minister Ariel Sharon's spokesman called it a "horrendous attack" and promised an Israeli response.

A neighbor, Rinat Cabra, said there were seven children in the family living in the house, and that the father was not home.

A settler, Yaacov Heiman, told Israel Radio that one of the dead was a young boy. "We heard screaming. We closed the house and then the army started to come," he said. "It's a horrible feeling."

Itamar, where some of the most militant Israeli settlers in the West Bank live, is not fenced in. Settlers insist the whole West Bank belongs to the Jews. On May 29, a Palestinian gunman attacked a high school at the settlement, killing three Israeli teenagers who were playing basketball.

In the claim of responsibility, the caller told The Associated Press the attack was in response to the arrest of a PFLP leader and Israel's attempt to separate the West Bank from Israel.

Israel Radio said Sharon left a public event when he was told of the attack and convened top advisers at his Tel Aviv office.

"This is a horrendous attack, and there always has to be a response for such things," said Sharon's spokesman, Raanan Gissin.

On Thursday, Palestinian leader Yasser Arafat condemned attacks against Israeli civilians, but Palestinian officials have always differentiated between Israelis not in the West Bank and those who live in the West Bank, claimed by Palestinians for a state.

The Associated Press contributed to this report.