RAMALLAH, West Bank ? Prime Minister Ariel Sharon said Israel was at war for its survival and vowed to smash Palestinian militants in an uncompromising offensive as he addressed a nation rattled by five suicide bombings in five days including back-to-back attacks Sunday that killed 15 Israelis.

Marking a widening of the operation in the West Bank, Israeli tanks entered Bethlehem early today, stopping 500 yards from the Church of the Nativity, which marks the traditional birthplace of Jesus, witnesses said. The incursion began at 5:30 a.m., just before sunrise. The Israeli military had no immediate comment.

Earlier, about 60 Israeli tanks, along with bulldozers, moved into Qalqiliya late Sunday, said the Palestinian governor, Mustafa Malki. The Israeli forces quickly took control of town, in the northern part of the West Bank next to the line with Israel. The military said troops were searching for suspects and weapons and intended to “destroy the terrorist infrastructure” in the town.

In Ramallah, under Israeli control since Friday, dozens of European peace activists, their arms raised and holding white flags, marched past Israeli soldiers surrounding Yasser Arafat’s office to join the Palestinian leader, saying they would stay with him as human shields.

Thirteen of the peace activists were arrested after they left Arafat’s office, the military said. The spokesman’s office said they could face charges of violating order closing Ramallah to foreigners.

At least 20 Palestinians and two Israeli soldiers had been killed in Ramallah since Friday.

Late Sunday, witnesses and Palestinian officials said Israeli soldiers opened fire on and killed five policeman when the Palestinians tried to surrender in Ramallah.

“We put our weapons at the main entrance and started to walk out when the Israelis fired on us,” said a policeman at the building who would only give his name as Omar. He said 17 police remained in the building and the standoff continued.

In a statement, the Israeli military said “wanted men” were in the building and one of them, wearing an explosives belt, opened fire on them. The soldiers chased him and shot him dead, the statement said.

The military statement also said that Israeli soldiers entered Ramallah Hospital to look for suspects, but “categorically denies false Palestinian claims of a mass murder and massacre at the hospital.” The military spokesman’s office said soldiers searched the hospital for suspects “while safeguarding the dignity of those within.”

In the north of Israel, Hezbollah guerrillas in Lebanon fired on Israeli troops in the second border incident in as many days. The Israeli military said it believed it shot two of the guerrillas. No Israeli soldiers were injured.

Earlier in the day, Israeli forces surrounding Arafat’s headquarters exchanged fire with Arafat’s guards, and Palestinian officials said Arafat was just a few yards from the fighting. Several guards were wounded, two of them seriously.

The Israeli army spokesman, Brig. Gen. Ron Kitrey, acknowledged that Arafat was at risk, even if he was not a target.

Addressing the nation in a five-minute televised speech, Sharon said Israel is fighting a “war over our home” and branded Arafat an enemy of the Jewish state and the “entire free world,” as well as a danger to the Middle East.

“We must fight against this terrorism, fight with no compromise, pull up these wild plants by the roots, smash their infrastructure, because there is no compromise with terrorism,” Sharon said, adding that only then a cease-fire would be possible.

Palestinian Cabinet Minister Saeb Erekat said the speech was “void of substance, void of hope, void of realism.” Erekat said Sharon “slammed the door tonight in the face of all of those who are trying to de-escalate.”

The Cabinet met Sunday to review plans for the next stage of the offensive, for which 20,000 reserve soldiers were mobilized.

In the first of Sunday’s two suicide blasts, a Palestinian from the Islamic militant group Hamas blew himself up in a restaurant in Haifa, killing himself and 15 diners, and wounding more than 40.

The blast tore away much of the roof and shattered tables and windows. Twisted piles of metal covered the floor. “Even the moderately injured were on fire,” said a witness, Shimon Sabag, who helped administer first aid.

Two hours later, a suicide bomber walked into a paramedics’ dispatch station in the Jewish settlement of Efrat in the West Bank and detonated his explosives. The attacker died and four medics were wounded, including a trainee who was in serious condition.

President Bush, who has defended Israel’s offensive, condemned Sunday’s bombings and said they would not “deter him from the pursuit of peace,” White House spokesman Gordon Johndroe said.

Israel’s ambassador to the United Nations said U.S. officials have suggested to Israel that it would not have to act immediately on a U.N. Security Council resolution passed Saturday, since its call for Israel to withdraw from Palestinian territory had no timetable. “Everyone is aware of this, including the Americans,” the ambassador, Yehuda Lancry, told Israel Army Radio.

In Ramallah, the Palestinians’ commercial center, Israeli troops commandeered homes and buildings, set up sandbag emplacements draped with camouflage netting on residential streets, erected barricades and dug trenches, making the hilly streets into a near-impassable maze.

There were sporadic exchanges of fire. Reporters saw two bodies of Palestinians lying in a street in the center of the city, near 15 Palestinians kneeling against a wall under Israeli army guard. Soldiers moved house-to-house and in one case herded several handcuffed Palestinian policemen into a military vehicle.

Israel has been trying to isolate Arafat, confining him to a three-floor building in the sprawling government compound in Ramallah.

In the building Sunday, a smiling Arafat hugged the peace activists visiting him. Israeli-Canadian, Netta Golan who has been living in Ramallah for the past few months, was among 30 activists who said they would remain with Arafat as human shields.

“I know that the only chance for Israelis to have peace and security is for the Palestinians to have peace and security,” Golan, 30, said in a telephone interview.

Israel declared Ramallah a closed military zone and said foreigners, including journalists, would be removed. The Foreign Press Association in Israel issued a protest, saying media must be allowed to cover a major story.

Anthony Shadid, a Washington-based Boston Globe reporter, was shot in the shoulder Sunday while standing in the doorway of a Ramallah shop, Globe foreign editor James F. Smith said. Shadid was conscious and in stable condition in a private Arab hospital in Ramallah, Smith said. It was not clear who shot him and the Israeli army was investigating.

Violence erupted in September 2000, destroying peace negotiations and helping bring the hardline Sharon to power. In the past 18 months, 1,269 people have been killed on the Palestinian side and on 416 on the Israeli side.