Israeli authorities filed at least 3,449 demolition orders against structures put up without permits in West Bank settlements over the past decade, but demolished only 107 - or 3 percent - according to the report from Peace Now, which tracks the growth of settlements.
The report was based on statistics from the Israeli military, which is responsible for enforcing building laws in the West Bank, Peace Now said. A military spokesman declined to comment on the report.
Israel has not officially built new settlements since the 1990s, and Israeli Prime Minister Ehud Olmert recently reiterated his support for that policy. But West Bank settlers have thrown up more than 100 unauthorized settlement outposts in the past decade, some of them on land privately owned by Palestinians, often with the tacit or active cooperation of Israeli authorities.
Israel and the Palestinians agreed last week at a U.S.-sponsored conference in Annapolis, Maryland, to relaunch peace negotiations. Both sides have said they will carry out their commitments under a U.S. peace plan known as the road map.
For the Palestinians, that means cracking down on militant groups, while for Israel obligations include dismantling several dozen illegal outposts and freezing all settlement construction.
Israel's actions on the ground contradict its commitments, the Peace Now report charged.
"On the one hand Israel commits itself to not building new settlements and not developing existing ones - something it carries out on paper. But in practice, construction is continuing energetically, only now it's called 'illegal,' and goes on undisturbed," according to the report.
Mark Regev, an Israeli government spokesman, did not directly address the report's findings but said Israel would do everything required of it by the road map.
"Israel is committed to all of its obligations under the road map and will be implementing every last one of those obligations, just as we expect the Palestinians to fulfill theirs," Regev said.
The numbers obtained by Peace Now show that settlers have built illegally in official settlements as well as unauthorized outposts, with minimal intervention from police. The illegal structures include houses, gas stations, and cellular antennas.
Nearly 270,000 Israelis live in settlements in the West Bank and another 180,000 live in Israeli-annexed east Jerusalem, alongside 2.4 million Palestinians. The Palestinians claim all of the West Bank as part of a future independent state, and want to make east Jerusalem their capital.
A report released last month by Peace Now found that construction is ongoing in 88 of the 122 officially authorized West Bank settlements.