nder heavy cover fire from helicopters, Israeli troops combed this refugee camp for weapons and gunmen Tuesday in the biggest Gaza offensive in years. Twenty Palestinians were killed, including two teenagers shot as they gathered laundry.
International condemnation mounted of the operation, and the United States said it was asking Israel for ''clarification.'' The United Nations and European Union demanded an end to the incursion, which Israeli security officials said would last at least a week.
In Rafah, a crowded camp of 90,000 people near the Egyptian border, Palestinian families sought refuge from the rocket and machine-gun fire in the innermost rooms of their homes.
Electrician Khaled Al-Assar, 38, said he sat with his wife and five children in one room of their house as gunfire rattled all around and a missile landed nearby, shattering windows.
''The kids were terrified, there was very loud boom, they started screaming and crying,'' he said.
Not everyone stayed inside, and the consequences could be deadly. Ahmed Mughayer, 13, and his sister Asma, 16, were killed by Israeli fire when they ventured onto the roof of their three-story apartment building to bring in laundry, their father Mohammed said.
Mughayer said his wife had told Asma not to go out because of the shooting. ''Asma said, 'Don't worry, I'll be careful,''' he said.
The Israeli army said the aim of ''Operation Rainbow'' was to destroy weapons-smuggling tunnels and arrest Palestinian militants. It said it did not intend to demolish large numbers of Palestinian homes. Troops tore down four homes Tuesday, witnesses said.
Last week, Israel destroyed about 100 houses, making more than 1,000 Palestinians homeless…