Nidal Eid was praised by Hamas officials as an example of anti-Zionist resistance when he managed to build a house here last year despite an Israeli blockade that barred the import of any building materials. But earlier this week, his house was the first to be demolished by the Hamas government, which said it had been illegally built on public land.

Bulldozers, accompanied by Hamas forces and police officers who beat residents with sticks, razed at least 25 houses, including some concrete structures here in Rafah, the southernmost city of Gaza.

“A bulldozer placed its shovel on the house and the policemen said we have 10 minutes to leave the home,” said Mr. Eid, 30, a father of nine, the youngest of whom was 15 days old when the house was destroyed.

In a scene reminiscent of those 16 months ago, after the Israeli invasion of Gaza, people could be seen sitting on the debris of their houses or in tents, some women burying their faces in their hands. Crowds gathered to offer comfort to relatives or just to witness the demolitions.

Issa al-Nashar, the mayor of Rafah, said that building on government land “requires an approval from the Lands Authority in addition to a license from the municipality.” Both are controlled by Hamas, the radical Islamist group that seized power in the coastal enclave in 2007.

Hamas’s campaign to remove what it calls “aggressions on public properties” coincides with the 62nd anniversary of Israel’s creation, known to Palestinians as the Nakba, or catastrophe. More than 700,000 Palestinians fled or were driven from their villages and towns to the West Bank, Gaza and neighboring states.

“This is the Nakba of 2010,” said 52-year-old Subhia al-Ghazawi, who moved to Rafah from Gaza City after her house was damaged in Israel’s three-week invasion, which Israel said was aimed at stopping rocket fire into southern Israel. That war destroyed or damaged thousands of homes and left tens of thousands of people homeless.

Since coming to power, Hamas has generally praised any housing construction as a challenge to the sanctions that were imposed in a bid to isolate and defeat the new Gaza government.

After the war, Hamas encouraged homeless people to use mud bricks to build makeshift shelters, and Mr. Eid said that he “taught Hamas how to build houses from clay.”

The idea that Hamas is now destroying some of those few homes has shocked people here.

“We lost all our belongings when the house we rented was destroyed in the war, so we decided to settle here,” Ms. Ghazawi said, sitting in a tent set up next to the remains of her three-room house.

Mukhaimar Abu Sada, a professor of political science at Al-Azhar University in Gaza City, called the demolition of houses “unacceptable” and said it reflected the troubles Hamas was having in changing from a resistance movement to governing. “If Hamas had thought this step through, it would not have taken it,” he said. “Though preventing the seizure of government land is something required, the timing is wrong.”

Mimi al-Huwari, 60, is an Egyptian who lived for two years in “a room, kitchen and a toilet built with the help of the good doers” after her Palestinian husband divorced her. Now that her house has been destroyed, she said, “my family is in Egypt, and I don’t have anybody here. I have a son whose one-room home is barely enough for his six-children family.”

So far, Hamas officials are not backing down or admitting any errors. Mr. Nashar, the mayor, said “the Nakba is one thing, and the law is something else.” He said the land had been allocated for the rebuilding of a religious school, which was destroyed in an Israeli airstrike during the war. He said the Ministry of Sport also had plans for the site.

Last week, coincidentally, Hamas began a project to build 1,000 houses that could be readily expanded when cement and construction materials became available for large-scale rebuilding.

But the ousted homeowners will not be easily mollified, and they question why the government failed to step in last year when they bought the land from a local clan. Mr. Nashar said it was an oversight, that the municipality had granted more than eight acres to the clan, “but some people from the family sold the nearby government land to people.”

Meanwhile, Hamas executed three Palestinians convicted of murder, the Interior Ministry said Tuesday.

In April, for the first time since taking over Gaza, Hamas executed two people accused of aiding Israel, but Tuesday’s executions were the first against people found guilty in criminal killings. A firing squad conducted the executions at dawn.