Jerusalem ? A Palestinian suicide bomber slipped into a Jewish settlement in the West Bank Saturday night and blew himself up in an outdoor food court amid scores of young Israelis. He killed himself and at least two Israelis and injured more than 20 others.

It was believed to be the first time a suicide bomber had penetrated the heavily guarded perimeter of a Jewish settlement and detonated a bomb.

The bombing occurred at the end of an exceptionally violent day. At least four other Palestinians were killed, one of them a senior militant of the Islamic Resistance Movement, known as Hamas, who died when a car near him exploded in what the group said was an assassination by Israel.

Saturday night’s bomb, packed with nails, exploded outside a crowded pizzeria at the open-air shopping plaza in Karnei Shomron, a settlement of about 5,300 Israelis between the Palestinian cities of Qalqilyah and Nablus in the northern West Bank.

The blast took place a little before 8 p.m. at the end of the Jewish Sabbath, when many youths go out for a bite to eat or a stroll with friends.

Witnesses described a scene of carnage as teen-agers who moments earlier had been ordering pizza and soft drinks and chatting in the cool evening air were suddenly scattered on the plaza’s floor, many of them bleeding and badly injured.

Ambulances, police and soldiers raced to the scene, as did parents looking for their children. The pizzeria was shattered, its ceiling tiles hanging, its windows blown out and blood on its floor.

The Popular Front for the Liberation of Palestine, a militant group that has carried out other attacks on Israelis, took responsibility for the blast, according to the Arabic language satellite television network al-Jazeera.

Also Saturday, Palestinians fired two rockets at Israeli positions, one in the Gaza Strip and one just outside of it. The rocket that landed inside Gaza hit an Israeli army base but caused no casualties.

Israel has vowed to strike back harshly in response to the rockets, which it regards as a serious new Palestinian threat. Manufactured by Hamas, the rockets are inaccurate and crudely made, but because some of them have a range of five miles or more, they pose a threat to a number of Israel’s cities as well as its main international airport.

In Gaza Saturday, three Palestinians were killed when Israeli troops and Palestinian militants fought gun battles.