Israeli governments have consistently failed to follow their own laws and guidelines for land confiscation and building in the occupied West Bank, an official report said on Wednesday.
The study, published by the state comptroller, said it found "serious and continuous improprieties" in preventing construction illegal under Israeli law on land captured in the 1967 Middle East War.
The World Court brands all Israeli settlements on occupied land illegal. Israel disputes this.
The 400-page report said laws on illegal building had not been enforced strictly enough for either Israelis or Palestinians living under Israeli administration.
"Cases were found where the administration allocated thousands of dunams of land for (Jewish settlement) without due process," the report by Comptroller Micha Lindenstrauss said.
"Since 1993 the administration has ceased registering state land, yet continued to confiscate land without putting it through the registration process," it said. A dunam equals 1,000 square metres.
Israel recently finished removing 9,000 settlers from the Gaza Strip and northern West Bank under a plan to "disengage" from conflict with the Palestinians, but some 245,000 settlers remain in the West Bank, home to 2.4 million Palestinians.
The report echoed criticism by a government-appointed investigator who said in March that 105 Jewish settler outposts had been built without Israeli government permission and had spread with state funding and military protection.
Israel has said it will remove many unauthorised outposts under a US-backed peace "road map," but has yet to comply. Palestinians have failed to meet their own obligation to start disarming militant factions.
Defence officials failed to prevent more than 70 percent of cases of illegal construction by Israelis and more than 55 percent of that by Palestinians in the West Bank from 2000 to November 2004, the comptroller's report said.