Israeli tanks and troops attacked Palestinian positions in Gaza and Bethlehem early Friday, killing a top commander and 23 other Palestinians, officials and witnesses said. A gunman infiltrated a Jewish settlement earlier in Gaza and killed five Israelis.

The violence, which followed a day of intense Israeli strikes throughout the Palestinian territories Thursday, came hours after President Bush announced he was sending Mideast peace envoy Anthony Zinni back to the region next week.

Early Friday, 20 Palestinians died in two Israeli attacks in Gaza, including Maj. Gen. Ahmed Mefraj, deputy commander of public security, the highest-ranking Palestinian officer to be killed in a clash with Israelis.

He was one of 16 killed and 35 wounded when Israeli forces moved into Hozaa village next to the central Gaza city of Khan Younis early Friday, Palestinians said. Palestinians said a tank shell and machine gun fire hit his car, killing Mefraj and a bodyguard.

The Israeli military confirmed that troops had entered the village, "a center of activity of several terror organizations," exchanged fire with Palestinians and made several arrests. Troops began pulling out at daybreak, residents said.

North of Gaza City, Israeli gunboats and helicopters attacked a Palestinian police base, killing four people and wounding six others, doctors said. Three missiles were fired at the base, witnesses said.

Israeli forces also entered Bethlehem from two directions early Friday, Palestinians said. Israeli helicopters fired at the Aida refugee camp after Palestinians shot at an Israeli outpost nearby, witnesses said. Four Palestinians were killed and 20 wounded, Palestinians said.

As news of Mefraj's death spread Friday, hundreds of gunmen converged on Nasser Hospital in Khan Younis, firing rifles in the air and calling for revenge against Israel.

The Israeli strikes came after a Palestinian gunman attacked the Atzmona settlement in southern Gaza late Thursday, opening fire with an assault rifle and throwing grenades at a high school. Four Israeli were killed and 20 wounded, the military said. One of the wounded later died in a hospital. The gunman was shot and killed, Israeli officials said.

Israel Radio reported that the military wing of the militant Hamas organization claimed responsibility and identified the attacker as Mohammed Farhat, 19, from Gaza City. The attacker entered the settlement from the south, near the Palestinian city of Khan Younis, according to the radio report.

"I was watching television when I heard gunfire outside very close," Elisheva Weiss, a resident of Atzmona settlement, told Israel Radio. She said settlers were instructed by loudspeaker to stay in their homes and keep their lights off.

In other violence Thursday, 13 Palestinians were killed as Israeli troops stormed through two West Bank refugee camps before dawn and rocketed a police station after nightfall in one of Gaza's most crowded camps. Additionally a Palestinian suicide bomber was killed Thursday.

In Bethlehem late Thursday, an Israeli warplane fired a missile at Palestinian headquarters, a complex hit hard in previous air strikes. The Israeli military said it attacked a military security building as part of its "efforts to prevent terrorism."

In announcing Zinni's return, Bush called for both sides to end the fighting. He said the Israelis had to show "a vision for peace. There's got to be more than security." Bush said, however, he fully supported Israel's right to defend itself from Palestinian attacks.

He called on Palestinian leader Yasser Arafat to make a "maximum effort to end terrorism against Israel."

Israeli and Palestinian leaders welcomed Zinni's planned return. "Prime Minister (Ariel) Sharon values and appreciates the work of General Zinni and the efforts he has made in halting the violence, terror and incitement," a statement from Sharon's office said.

Palestinian negotiator Saeb Erekat said the Bush administration had reached the conclusion that Sharon's policies were leading to "more bloodshed and deterioration." He hoped Zinni would bring a "concrete plan" to carry out agreed-on plans for a truce and resumption of peace talks.

Israeli leaders said Thursday that the latest campaign was aimed at forcing the Palestinians to stop terror attacks, but it has not had that effect so far.

A Palestinian suicide bomber walked into a Jewish settlement's hotel complex in the West Bank and blew himself up in the lobby, injuring four people.

Another suicide bombing was thwarted at a Jerusalem cafe when the restaurant owner, a waiter and a customer jumped the man, shoved him outside and grabbed his bag after they saw wires dangling from it.

In the northern Israeli city of Pardes Hanna, a resident spotted a suspicious object in a shopping center and called police. As a bomb disposal team approached, the bomb exploded, police said. No one was hurt.

Sharon, stung by an earlier rebuke from Secretary of State Colin Powell, responded that the conflict was "imposed on Israel by the Palestinian Authority and its leader."

"Israel has never declared war on the Palestinians. Israel fights back against terror organizations in the framework of its right of self-defense. He who started this war has the power to stop it, but continues to prefer a war of terrorism," Sharon's office said in a statement.

A defiant Arafat insisted Palestinians would not be cowed by the escalating strikes.

"No one can shake the Palestinians," he told reporters in the West Bank town of Ramallah on Thursday, hours after Israel fired missiles at his headquarters complex for the third night in a row. "If the Israelis believe that they can frighten them by tanks or by missiles or by Apaches (helicopter gunships), then they are mistaken."

Sharon ordered the military strikes, among the most intense and wide-ranging of the 17-month-old conflict, after more than two dozen Israelis were killed last weekend in a string of Palestinian attacks.

About 80 tanks and armored vehicles entered the town of Tulkarem late Wednesday and surrounded the adjacent refugee camps of Tulkarem and Nur Shams. Twenty-four hours later, gunmen and soldiers were still exchanging fire. At least nine Palestinians were killed, including a rescue worker, Palestinians said.

U.N. Secretary-General Kofi Annan condemned the killing of the aid worker and called on Israel to investigate the incident.

In the West Bank village of Siris, Israeli forces killed a leader of the militant Islamic Jihad, Mohammed Anani, 27, who opened fire on soldiers as they approached his home, witnesses said. Anani had been wanted by Israel for involvement in suicide bombings.

Israeli warplanes fired missiles at a Gaza City complex, wounding at least eight. In central and northern Gaza on Thursday, two Palestinians were killed in gunbattles with Israeli troops, Palestinian doctors said.