JERUSALEM — An Israeli watchdog group, citing leaked military data, charged yesterday that nearly 40 percent of the land on which West Bank settlements were built was private property seized from Palestinians — challenging Israel’s long-standing assertion that the communities were built only on unclaimed territory.Meanwhile, in the Gaza Strip, troops killed a top Hamas commander in the latest military operation against Palestinian rocket squads, as troops operated in two areas of northern Gaza. Another Palestinian died of gunshot wounds hospital officials said.

Also Tuesday, in apparent Palestinian infighting, a former Fatah Cabinet minister, Abdel Aziz Shahin, 62, was shot and wounded in Gaza City just after criticising the ruling Islamic Hamas on a radio show, hospital officials said. His condition was not known.

Peace Now, an anti-settlement Israeli watchdog, unveiled a report it said showed that settlements had been built on Palestinian property seized by the army, long after the Israeli Supreme Court outlawed the practice in 1979.

“We are talking about an institutional land grab,” Dror Etkes, a settlement expert with Peace Now told a press conference in Jerusalem. Peace Now said its charges were based on information leaked from the Civil Administration, the Israeli military department responsible for administering civil affairs in the West Bank, which Israel seized in the 1967 Middle East war. It said at the government’s request, the Supreme Court delayed a scheduled May hearing on Peace Now’s petition to have the data released under freedom of information laws. In its 174-page report, Peace Now said the Civil Administration database showed that 38.8 percent of the area currently occupied by Israeli settlements, settlement outposts and industrial zones in the West Bank was privately owned Palestinian land, illegally expropriated by Israeli authorities.

Most notable was the city of Maaleh Adumim outside Jerusalem — with a population of 30,000 the West Bank’s biggest settlement — where Peace Now said 86.4 percent of the real estate was in fact Palestinian-owned. Israel has agreed to freeze settlement construction under the terms of an internationally backed peace plan, and under pressure from the United States, but says the ultimate fate of the settlements should be left to future peace negotiations.

The court ruling of 1979 ordered the Defense Ministry to stop seizing private Palestinian land for military use and then turning it over for settlement construction. Peace Now said the practice continued nonetheless, and 31.3 percent of the land built into settlements since the ruling is owned by Palestinians.

Civil Administration spokesman Shlomo Dror said he had not yet had an opportunity to study the report and so could not confirm or deny the figures. “I can say that in general we have a clear directive not to build on privately-owned Palestinian land,” he said. He added that West Bank property records had passed down through successive Ottoman, British and Jordanian rulers before reaching Israeli hands, were incomplete and that some people listed as holding property titles had since died and their heirs were unknown.

“I’m not sure that all the land Peace Now says is Palestinian, is Palestinian,” he said.

Bentsi Lieberman, head of the settlers’ council, told Channel 2 TV that the report was wrong — settlements were built on public land. He said much of the public land is claimed falsely by Palestinian individuals, creating confusion reflected in the Peace Now report.

Nearly 244,000 Jewish settlers live in the West Bank. In the summer of 2005, Israel evacuated all 8,500 settlers from the Gaza Strip, along with its military bases.

Since then, Palestinian militants in Gaza have been pounding southern Israel with homemade rockets. A woman in the town of Sderot, a frequent target, was killed in one such volley last week.

The Israeli military launched a three-pronged offensive in the northern Gaza Strip early yesterday, killing three Palestinians — a Hamas commander, an elderly woman and a 20-year-old watching a battle in a refugee camp, hospital officials said.