Israeli troops backed by helicopter gunships, tanks and bulldozers went street by street and house by house in one of the most densely populated neighborhoods of this city and adjacent refugee camp Tuesday, seeking to root out Palestinian fighters and weapons. Local hospital officials said 19 Palestinians were killed and dozens were injured.

Operation Rainbow, as the Israelis called it, was the biggest incursion into the Gaza Strip since the Palestinian uprising began nearly four years ago, military officials said. Terrified residents in the targeted area fled gunfire and missile attacks and suffered casualties.

A dozen or more houses were destroyed in the Tel Sultan neighborhood, where the heaviest fighting occurred, and dozens of others were damaged or scorched.

By nightfall, officials at Najar Hospital, the main medical center in Rafah, reported receiving the bodies of 19 dead Palestinians, including a young brother and sister, along with 62 injured, 25 of them seriously. The Israeli army reported no casualties among its troops and said that 17 of the 19 dead Palestinians were militants.

Palestinian officials condemned the attack as a deliberate assault on civilians and pleaded for international support, while Arab nations called for an emergency meeting of the U.N. Security Council. The United Nations and the European Union both demanded that the incursion be stopped, and EU envoy Marc Otte was in Israel for talks with diplomats and security officials, news services reported.

Abu Qusay, identified as a commander of the al-Aqsa Martyrs Brigades in Gaza, a Palestinian group responsible for many suicide bombings inside Israel, told Freedom Radio in Gaza that his group would deliver "a very painful response" to what he called "the Zionist massacres."

Israeli officials said international criticism was based on the misconception that the army was on a mission to demolish the houses of innocent civilians. "We have no policy of destroying houses," said Avi Pazner, a government spokesman, adding: "You have in Rafah now an industry of terror. We want to stop that for our good and also for the good of the population of Rafah who are being terrorized."

Uzi Landau, a Likud Party minister, said Israel's treatment of civilians in Rafah compared favorably to the actions of U.S. and British forces who have caused the deaths of hundreds of civilians in Iraq. "I guess we are at least as careful as those who are trying to tell us how we should protect our people," he said.

The scene at Najar Hospital was one of chaos, with screaming ambulances ferrying the dead and wounded, who were hauled and shoved through a noisy mob of hysterical relatives and outraged residents into the overcrowded emergency room. The small morgue was quickly overrun, officials said, and bodies were sent to nearby shops for temporary storage.

Just inside the front door of the hospital, Ahmed Hussein, 11, lay on his side, pursing his lips to keep from crying as a male nurse stitched a hole in his left shoulder where he had been shot. His uncle said the boy had opened a living room window to sneak a look at the fighting outside when he was hit by a bullet. His mother was also wounded.

The boy's uncle, Tamim Hussein, said Israelis soldiers had entered the tallest houses in the area and set up sniper positions. "They go up to the roof, make a hole in the wall and shoot from it at anyone who's moving," he said. He saw three bodies in the street in the morning that no one could reach for several hours because of the shooting.

Leaning against a wall near Ahmed Hussein's bed was a paramedic ambulance worker, Eyad Foudah, 32, who was catching his breath after working 28 hours without a rest. He said the two ambulances he works with had carried 17 wounded and eight dead to the hospital since Monday evening. Among them were a young brother and sister, both shot in the head as they sought to take down laundry from a second-story balcony. The two were dead when he arrived, he said, and their family had laid them out on mattresses.

Hospital officials identified the victims as Ahmad and Asma Mougheir. Some reports put their ages as 10 and 11, others as 13 and 16.

Foudah, whose blue smock and pants were smeared with dried brown bloodstains, said soldiers had prevented his ambulance from entering Tel Sultan for an hour to 90 minutes each time it returned for more casualties. "Before they let us in, we have to empty all the things from inside and put them on the ground, raise our hands and lift up our shirts" he said.

Capt. Jacob Dallal, an Israeli military spokesman, said the army was investigating the deaths of the children. "We don't know exactly what happened there," he said.

As for the ambulance delays, Dallal said all ambulances are subjected to security checks because gunmen have used them to launch attacks and smuggle arms. He blamed the long delays on the fact that the ambulances were seeking to enter combat zones where firing was going on and some roads were booby-trapped with mines. "In a situation like this, also an ambulance passing by could be hurt," he said.

Operation Rainbow began Monday, when tanks and armored personnel carriers sealed off the Gaza Strip's southernmost city and refugee camp, with a population of about 165,000. Just after midnight, helicopter gunships fired missiles at areas where large numbers of fighters were allegedly concentrated, killing three people and wounding seven, as soldiers started moving into Tel Sultan, which they encircled and cut off from the rest of Rafah.

A few hours later, an attack helicopter fired two missiles at militants near a mosque, killing eight people and wounding 23. The mosque was damaged in the attack, witnesses said.

By dawn residents reported several gun battles. But for the most part, Tamim Hussein and other Palestinian witnesses said, armed Palestinians did not put up much of a struggle against the tanks and overwhelming numbers of soldiers arrayed against them.

The Israeli army chief of staff, Lt. Gen. Moshe Yaalon, told reporters that soldiers had demolished three houses overnight that concealed tunnels used for smuggling weapons across the nearby border with Egypt. He said the army could take several days to complete its mission.

[Two gunmen from the al-Aqsa Martyrs Brigades were killed early Wednesday in fighting in the West Bank cities of Nablus and Jenin, news services reported.]

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

A Palestinian man is comforted as he stands by an ambulance after a relative was killed by an Israeli sniper during a major offensive in the Rafah refugee camp. Israel launched its biggest incursion into densely populated areas of Gaza since the beginning of the nearly four-year-long Palestinian uprising.