IN NUR SHAMS REFUGEE CAMP, WEST BANK Moving quietly through the alleys of this ramshackle neighborhood, the Israeli soldiers forced their way into Iyad Abu Shilbaya's home in the early morning hours under cover of darkness.

A Hamas operative who had been detained repeatedly by the Palestinian Authority and imprisoned for two years by Israel, Abu Shilbaya was one of more than a dozen people whose homes were raided during a sweep of arrests in the Nur Shams camp outside the town of Tulkarm on Friday.

But Abu Shilbaya was not arrested. In an encounter in his bedroom, the details of which remain murky, he was fatally shot at close range, prompting vows of revenge by Hamas and condemnation from the Palestinian Authority, which said the killing "undermines the credibility" of recently renewed negotiations with Israel.

The talks, which have broached core issues in dispute, have been accompanied by stepped-up violence from Palestinian militants opposed to the negotiations, including the fatal shooting of four Jewish settlers in the West Bank last month in an attack claimed by Hamas and rocket fire from the Gaza Strip into Israel.

The killing of Abu Shilbaya came at a time of improved cooperation between the Israeli and Palestinian security forces, but it was a reminder that Israeli troops still operate in areas controlled by the Palestinian Authority, and it raised fresh questions about the conduct of elite Israeli units when pursuing militants in the West Bank.

Following classified rules of engagement, the units who carry out the most risky arrests are authorized to use lethal force, which can cause political complications.

Ghassan Khatib, the spokesman for the Palestinian government in the West Bank, said actions such as the killing of Abu Shilbaya, which he called an assassination, damaged the Palestinian Authority's standing among its own people, giving it the image of a "sort of a subcontractor of the Israeli occupation."

"We make no secret of our cooperation with Israel, but such Israeli activities give the impression that this is collaboration, not cooperation," Khatib said. After Friday's killing, Hamas was quick to accuse the Palestinian Authority of complicity in the deadly raid.

Palestinian security forces detained Abu Shilbaya for a few days earlier this month as part of a mass roundup of Hamas militants after the killing of the Israeli settlers.

The Israelis have lately praised the performance of Palestinian security forces in the West Bank. But they say they need more assurances that the Palestinians can control security before the Israeli military hands over more responsibility in the area.

Accounts of how Abu Shilbaya was killed, in an operation that an Israeli military official said was carried out by the special forces unit Cherry, or Duvdevan in Hebrew, provide a glimpse of how the unit works in the West Bank.

Muhammad Abu Shilbaya, a brother of the slain militant, said that soldiers forced their way into his house before 3 a.m. and ordered him to lead them to his brother's home nearby. There the front door was broken open and soldiers entered the darkened home while Muhammad was ordered to turn and face a wall outside.

"I heard Iyad call three times, 'Who's there?' and seconds later I heard shooting," Muhammad Abu Shilbaya said. "Then it was quiet." The brother said that soldiers ordered him to sit on the floor inside the house, and they opened a stretcher to take out the body of the slain man.

An army statement said that the militant, who turned out to be unarmed, had run toward the soldiers "in a suspicious way" with his hands behind his back, and when he ignored orders to halt, the troops, who felt threatened, opened fire. A medical report from a hospital in Tulkarm said that Abu Shilbaya had been shot twice in the chest and once at the base of the neck.

In the militant's cramped bedroom two days after the shooting, a bloodied mat remained next to the bed, and blood was spattered on a bedsheet, the lower part of a wall and a radio on the floor. Three spent bullet cartridges had been found a few feet from the bed, the militant's brothers said.

Iyad Abu Shilbaya's wife, Latifa, who was visiting relatives on the night of the raid, said that the killing of her husband was completely unexpected, because he had not behaved like a wanted man on the run. "He was sleeping at home," she said. "They could have shot him in the leg and arrested him."

Relatives and neighbors said that soldiers gave no warning before entering Abu Shilbaya's home and did not call on him to surrender.

Capt. Barak Raz, an army spokesman, said that the soldiers were given intelligence information that Abu Shilbaya might be armed and fired "when they felt their lives were threatened." He noted that all the other arrests in Nur Shams that morning were accomplished without incident.

Sarit Michaeli, a spokeswoman for the Israeli human rights group B'tselem, said that it was demanding a military police investigation. B'tselem has received no response from the army to its request for a similar investigation into the killing by Cherry soldiers of three militants in December in the city of Nablus, where witnesses said that two were shot as they came out of their homes with family members.

Raz declined to discuss the rules of engagement for the special forces units.

But a former soldier in Cherry who spoke on condition of anonymity said in an interview that the rules were "very fluid" and changed according to circumstances. The veteran, a member of the group Breaking the Silence, which publishes accounts by discharged soldiers who served in the West Bank and Gaza Strip, said that in close encounters with militants, members of the unit were given broad discretion to open fire.

In one operation, he recalled, soldiers were told that their objective was an armed militant, and that "if you see a weapon near him, you shoot. If he makes any strange or sudden move, you shoot. Don't take a risk. If you shoot, you'll have backing."

"The culture of the unit was to arrest, but also not to take risks," the veteran said. In some cases, soldiers were given the message that "killing the terrorist was best," he added.

The former soldier said Cherry troops were trained for hair-trigger responses in face-to-face confrontations with militants who were usually described in pre-operational briefings as armed or likely to be armed, although many times they were not.

After bursting into a room, there's no chance to instantly check if a militant inside is hiding a weapon, the former soldier said. So, in effect, " your life's already in danger the moment you're in the room and there's someone on a bed," he said. "It's an impossible situation."