An Israeli helicopter gunship and a tank fired rockets and artillery shells at Palestinian protesters Wednesday as they marched toward a heavily populated neighborhood in the southern Gaza Strip. At least 10 Palestinians were killed and dozens wounded, many of them children, as explosives and shrapnel ripped through the crowd.

Witnesses and survivors said soldiers gave no warning before opening fire. After what witnesses described as deafening explosions, children screamed amid the blood and body parts. Some of the crowd panicked and ran, while others tried to sweep up the wounded and drag them to safety. Men raced through the crowd, cradling wounded boys in their arms and searching desperately for an ambulance or medical assistance.

Senior Israeli military officials confirmed that a rocket and tank shells were fired but insisted they were meant as warning shots and were not aimed at the demonstrators walking from the center of this city toward the Tel Sultan neighborhood, which was sealed off by Israeli forces for the second consecutive day.

The officials conceded that one or more of the rounds might have gone off-target, and the army chief of staff, Lt. Gen. Moshe Yaalon, and a large number of cabinet ministers and official spokesmen took to the airwaves within hours to express regret and sorrow over the incident.

An army spokesman, Capt. Jacob Dallal, said that soldiers in the tank that opened fire believed their lives were endangered and that intelligence sources asserted there were gunmen in the crowd. But Palestinian witnesses insisted there were no fighters or weapons among the marchers and that the tank was more than 200 yards away.

Five more Palestinians were killed in Tel Sultan on Wednesday as the army continued its house-to-house hunt for militants and weapons. Soldiers ordered all male residents from age 16 to age 50 to report to a police station, while members of militant factions were called on to surrender by waving white flags or risk being shot.

[In two incidents early Thursday, five more Palestinians were killed, the Associated Press reported. Three militants were killed in a missile strike in the Rafah refugee camp around midnight, doctors said. The military said a helicopter fired at gunmen approaching Israeli forces. Before daybreak, two militants were killed by a tank shell near the border, doctors said.]

The killings brought the Palestinian death toll to at least 39 in the past two days, the largest toll in a single military operation in Gaza in several decades. There were no reports of Israeli casualties.

Although Israeli tanks and snipers have ringed Rafah since early Monday, cutting off the city and the adjacent refugee camp from the rest of Gaza, most of the area had remained tranquil until Wednesday afternoon, when the Palestinian Authority and various militant factions issued a joint call for protest.

A crowd of demonstrators began gathering outside a mosque in the city center. Young boys waving flags and banners of the various militant factions were in front as the crowd started moving northwest on Bahar Street toward Tel Sultan, swelling in numbers and anger as it went.

By the time it reached the Zourob intersection, witnesses said, nearly 2,000 people were chanting slogans and shouting "Jihad!" and "God is great!" At a bend in the road, they spotted an Israeli tank in the distance and many hesitated, but those in front kept walking. Some threw stones toward the tank that fell well short of their target.

Suddenly, the tank opened fire, according to witnesses and survivors. The shell hit an electrical support and detonated, they said, sending razor-sharp fragments of the support structure and the shell casing through the demonstrators.

Said Zourob, 20, said he was with the group when the firing began. Five people fell from the first round, he said. Then the tank fired another shell, which was followed by missiles from a helicopter hovering overhead. "I was amazed I wasn't hit," said Zourob, whose blue denim shirt was dark with bloodstains.

"Everyone was in a state of shock," said Kahamis Shaer, 18, also part of the group. "I saw a guy with his head chopped off and another with his intestines hanging out. Some people ran away; others came to help."

In the chaos that ensued, victims were dragged back toward the intersection and piled into ambulances and cars. The vehicles raced to Najar Hospital, which for two days has functioned as a combination combat-zone field hospital and mortuary.

The Israeli military reported that seven people were killed, but hospital officials reported 10 fatalities, five of them children or teenagers.

The dead were placed in the hospital's overcrowded morgue, while most of the wounded were rushed to other medical facilities. Thirteen were taken directly to the European Gaza Hospital in nearby Khan Younis, most of them age 15 or younger, according to officials there.

The youngest was Ibrahim Awedin, 8, who had been hit in the left eye and was sobbing quietly. His 11-year-old brother, Nouh, lay in the next bed, with a shrapnel wound in his left leg. Attah Breaqa, 10, who was hit in both legs, lay in an adjacent ward, alongside Yousef Fadel, 15, whose stomach had been gouged by shrapnel.

The army's version of events, which officials stressed was based on a preliminary investigation, differed markedly from that of the witnesses. Its statement said a helicopter fired a single missile as a warning shot into an open area. Soldiers then set off warning flares, and when the crowd kept coming, fired machine guns and four tank shells at an abandoned building. "It is possible," the statement said, that the casualties "were a result of the tank fire on the abandoned structure."

Dallal, the army spokesman, said soldiers had not anticipated facing such a large crowd of demonstrators and were not armed with nonlethal riot-control weapons such as tear gas and rubber bullets. "It's not typical of the type of combat activity we usually see," he said.

Dallal said soldiers had spotted armed men in the crowd. He and other Israeli spokesmen also raised the possibility that one of the tank shells had inadvertently set off an explosive charge planted by Palestinians along the road, which he said was the scene of frequent exchanges of fire.

Yaalon, the chief of staff, defended the army, telling Israeli reporters at a briefing that no soldier had received orders to fire into the crowd. He said the incursion in Tel Sultan, known as Operation Rainbow, would continue. But senior army sources told Israeli television that the incident had been a tragic mistake that could force the army to reassess the mission.

Defense Minister Shaul Mofaz, a former chief of staff, said Palestinian terrorists had often used civilians for cover. "I'm deeply sorry about today's incident," he told reporters, "but no other army could conduct a 31/2-year campaign against terror and have fewer casualties."

But Naomi Chazan, a member of parliament from the opposition Meretz party, was one of many politicians who predicted that the incident would give fresh impetus to Prime Minister Ariel Sharon's plan to unilaterally pull out of Gaza.

"My feeling is it will be very difficult for the government to justify inaction," she said. "This is a confirmation of the fact that the occupation is a prescription for tragedy. It cannot go on."

Correspondent Robin Shulman and researcher Samuel Sockol in Jerusalem contributed to this report.

A man searches for medical care for a child as Palestinians rush to help those wounded when Israeli forces fired on demonstrators. A Palestinian woman, right, tries to find medical assistance for her wounded son in southern Gaza. "Everyone was in a state of shock," one witness said.