Ending an agreement to ease restrictions, the Israeli army reoccupied Bethlehem today and imposed a new, indefinite curfew on its 28,000 Palestinian residents, saying militants had used 95 days without a curfew to turn the West Bank town into a center of terrorism and launch Thursday's bus bombing in Jerusalem that killed the bomber and 11 other people.

Stores and houses were shuttered and streets were largely deserted as residents went back indoors after becoming accustomed to such ordinary pleasures as going for walks, shopping, going to school and socializing. Israeli tanks and armored personnel carriers took up positions at key thoroughfares, including just off Manger Square, and jeeps patrolled the streets.

The clampdown came as violence persisted in other West Bank cities and in the Gaza Strip. A senior British official with the United Nations was shot and killed during an exchange of fire between Israeli soldiers and Palestinian gunmen in the northern West Bank city of Jenin, hospital and other sources said.

Also in Jenin, a 10-year-old boy also was shot in the head and killed by Israeli troops, a hospital official said.

A Palestinian sniper in the Gaza Strip shot and killed an Israeli soldier, Sgt. Shigdaf Garmi, 30, as he cleared a path ahead of an Israeli armored vehicle, a military spokesman said. Israeli soldiers shot and killed an armed Palestinian militant who was dressed in a uniform similar to those worn by Israeli soldiers as he approached the Jewish settlement of Netzarim, south of Gaza City on the Mediterranean, an Israeli army spokesman said.

In Bethlehem, in swift response for Thursday morning's suicide bus blast, Israeli troops demolished the home of the man they said was responsible, Nael Abu Hilayel, 22, and arrested his father.

Under an Aug. 19 security agreement known as Bethlehem First, Palestinians had assumed responsibility for security in the town. In return, Israel had lifted the on-again, off-again curfew and withdrawn from the center of town. The agreement was a sort of pilot program that Israeli and Palestinian officials said could be expanded across the West Bank and Gaza Strip if it proved successful.

Little militant activity has been apparent in Bethlehem since the accord, and even Israeli military officials initially said terrorist cells had been eradicated from the town. But a senior military official, who declined to be quoted by name, said today the three-month lull and relative freedom in Bethlehem had attracted militants from Palestinian cities across the West Bank, most of which are under Israeli military siege.

Now, he said, "The situation is to become similar to the rest of the Palestinian cities on the West Bank. We will be present in Bethlehem for as long as we believe it's desirable. We'll operate freely, we will not let any Palestinian security officers operate in the city or use their weapons. It's not going to change in the future."

Residents sought to adjust to the renewed restrictions. Samir Kanan, 52, said he and six friends had received permits allowing them to travel to $25-a-day construction jobs in Jerusalem, where they had worked for about a month. But when they arrived at work early Thursday and heard about the bus blast, they went back to Bethlehem, realizing that Israeli retaliation would be swift and that they needed to get home ahead of it.

"He messed things up for us," Kanan said of Abu Hilayel, the bomber from Bethlehem, as he watched a few children kick a soccer ball in the deserted street but remain poised to dash indoors at the first sight of an Israeli soldier. "I was working and things were more relaxed. Before that, I was jobless for more than one year. Now we're not doing anything."

But other Bethlehem residents said the freedom they enjoyed for three months was an illusion.

"What do you mean, things were better?" said Mahmoud Salah, 55, an unemployed welder who was working on the fence in his yard in the south Bethlehem neighborhood of al-Khader. "The town was encircled, workers couldn't leave, farmers couldn't tend their fields, food was more expensive."

Salah said he did not resent the bomber for bringing renewed restrictions down on the entire town. "If we want our homeland, we have to sacrifice," he said, "and everyone has to sacrifice, the martyr with his body and the people with their steadfastness."

Mayor Hanna Nasser denied that Palestinian militants had taken shelter in his town. The suicide bomber was "a pretext to give credibility to the argument that Bethlehem is giving asylum to wanted people and to break the Bethlehem First agreement," he said. He added that the reoccupation and renewed curfew were "100 percent" driven by politics in Israel, which will hold elections Jan. 28.

Friends of the U.N. worker who was killed in Jenin identified him as Iain John Hook, who arrived three weeks ago to oversee reconstruction of a camp for the U.N.'s Relief Works Agency, which provides social services for refugees.

Some Jenin residents who were reached by phone said Hook was in his office when he was killed. Israeli security sources said he apparently was hit by a stray bullet from fighting that erupted nearby as Israeli soldiers arrested a wanted Palestinian. But Mohammed Abu Ghali, director of Jenin Hospital, said Hook was shot by an Israeli soldier and was dead when he arrived at the hospital about 2 p.m. with two gunshot wounds to the stomach.

"The Israeli army did not allow the U.N. ambulance to enter to evacuate him, so he bled to death," Abu Ghali said. He said Hook's body was brought to the hospital about an hour after the shooting, after workers broke through his office wall and spirited him out through another building.

An Israeli security official had a different version. "We got a report of an injured U.N. person, and [Israeli Defense Forces] then tried to bring in an Israeli ambulance to help and give medical attention and treatment," he said. "But as soon as the ambulance got there, we discovered he was dead. We did everything possible to get the injured man to a hospital to receive medical treatment."

Correspondent Molly Moore in Tel Aviv contributed to this report.

An Israeli army platoon moves into Bethlehem in response to a bus bombing Thursday in Jerusalem in which 12 people were killed, including the bomber.