A suicide bomber blew himself up in a supermarket at the entrance to a Jewish settlement in the West Bank on Thursday, killing himself and wounding four bystanders, police said. One of the wounded was in serious condition.

The blast went off at the entrance to the Ariel settlement, one of the largest in the West Bank.

The radical group the Popular Front for the Liberation of Palestine claimed responsibility.

The bombing came only hours after a Palestinian carrying a bomb was overpowered by two patrons when he tried to enter a cafe in a trendy part of Jerusalem.

The two men blocked the man from entering the cafe and seized a backpack that had wires hanging out of it, Jerusalem Police Chief Micky Levy said. The men disconnected the wires and prevented the bomb from going off, he said.

The incidents occurred as Israel widened its assault on Palestinian targets, raiding two West Bank refugee camps and shelling Palestinian police positions. Late Wednesday, Israel fired missiles at Yasser Arafat's headquarters as he met the European Union's Mideast envoy. The blast blew out windows in the room where the two met moments before.

Eight Palestinians were killed and more than 20 injured in the fighting.

A defiant Arafat said Palestinians would not be cowed by the intensifying Israeli strikes.

"No one can shake the Palestinians," he told reporters in the West Bank town of Ramallah. "If the Israelis believe that they can frighten them by tanks or by missiles or by Apaches (helicopter gunships), then they are mistaken."

Israel's stepped-up military strikes drew unprecedented criticism from the Bush administration, which until now had backed Prime Minister Ariel Sharon, saying Israel had the right to defend itself against attacks by Palestinian militants.

Referring to Sharon's statements this week that force would replace diplomacy and that Israel would strike relentlessly to crush Palestinian militants, Secretary of State Colin Powell told a Congressional committee: "If you declare war on the Palestinians and think you can solve the problem by seeing how many Palestinians can be killed, I don't know that leads us anywhere."

Sharon's office said in response that Israel has not declared war on the Palestinians and that the conflict "was imposed on Israel by the Palestinian Authority and its leader."

The Palestinians asked for immediate U.S. intervention. "They (the Israelis) are imposing a daily war against our people, our leadership and the peace process," said Arafat adviser Nabil Abu Rdeneh.

Sharon ordered the military strikes after more than two dozen Israelis were killed last weekend in a string of Palestinian attacks. The prime minister has come under sharp attack at home for not offering Israelis a way out of their malaise. The past week has been one of the bloodiest in 17 months of fighting, with 80 Palestinians and 31 Israelis killed.

A key target in the new Israeli campaign has been Arafat's compound in Ramallah, to which he has been confined since December. Israeli helicopter gunships fired missiles at the complex for three straight nights, including late Wednesday, when two rockets struck several minutes apart.

At the time, Arafat was meeting in his office with Miguel Moratinos, the EU envoy to the Middle East. "We don't know where it hit, but it was very, very close," said the envoy's spokesman, Javier Sancho. The lights went out and the EU delegation was escorted out by flashlight, Sancho said.

Arafat adviser Ahmed Abdel Rahman said that the windows were blown out in the room where Arafat and Moratinos had met just moments before.

Israeli Foreign Minister Shimon Peres was speaking to Arafat by phone at the time of the air strike, Arafat's advisers said. Arafat held out the phone and told Peres "Do you hear this?" when one of the missiles hit, the aides said. Peres, who has been saying publicly that force alone cannot bring about a resolution, declined comment Thursday.

In the West Bank, about 80 tanks and armored vehicles entered the town of Tulkarem and surrounded the adjacent refugee camps of Tulkarem and Nur Shams, meeting resistance from dozens of Palestinian gunmen, witnesses said.

In the Tulkarem camp, Israeli troops seized a U.N.-run school as a command post, said Hamdi Dardouk, the Palestinian intelligence chief in Tulkarem.

Five armed Palestinians were killed in the fighting, doctors said.

In the West Bank village of Siris, Israeli forces killed a leader of the militant Islamic Jihad, Mohammed Anani, 27, who tried to shoot at soldiers as they approached his home, witnesses said. Anani had been wanted by Israel for involvement in suicide bombings and had served time in Palestinian jails.

Also Thursday, Israeli warplanes fired missiles at the Palestinian government complex in Bethlehem and the police headquarters in Gaza City. The Gaza City complex had been hit many times before. After Thursday's strike, only two of 25 buildings in the compound remained standing. The missiles sent rubble and glass flying hundreds of yards, and eight people were wounded. Children at a nearby school ran from the area.

Two Palestinians were killed in gun battles with Israeli troops in central and northern Gaza on Thursday, Palestinian doctors said. Two other Palestinians were shot dead by Israeli troops late Wednesday as they tried to lay explosives, the army said.

Also Thursday, Israeli gunboats fired missiles at a Palestinian police roadblock near the Gaza City coast and wounded 13 policemen, three critically, Palestinian security officials said. Other gunboats fired at Arafat's seaside office. The Israeli military said its forces attacked "terrorist targets" including a police post.

Throughout the Gaza Strip, Palestinian police closed roads around security installations Thursday and evacuated schools and government ministries for fear of more air strikes.