Jewish settlers have started building more than 600 homes in the West Bank since a building freeze expired last month, an Israeli pressure group says.
The pace of building is four times faster than before the ban was put in place, Peace Now says.
Recently re-launched Middle East peace talks could collapse over Jewish settlement building on occupied land.
Palestinian leader Mahmoud Abbas has vowed to leave the talks unless Israel renews its partial construction freeze.
More details on the 600-plus new homes being built by Jewish settlers will be released in a report on Monday, Yariv Oppenheimer, a spokesman for Peace Now, told the BBC.
Another Peace Now official, Hagit Ofran, added:
"I estimate that work has started at about 600 housing units [since the end of the construction freeze], and I'm looking to complete the survey in order to know the exact number, and it is [at] different stages of construction. In some places, it is only levelling the ground that has started and in others, it's the very foundation that is now being dug".
A separate count by the Associated Press news agency estimated that ground had been broken on at least 544 new West Bank homes since 26 September, when Israel lifted its 10-month freeze on most new settlement building in the West Bank.
Palestinian spokesman Ghassan Khatib said the figure was "alarming and is another indicator that Israel is not serious about the peace process, which is supposed to be about ending the occupation".
But Israeli government spokesman Mark Regev said Israel wanted to "proceed to move forward in the peace process and all the difficult issues, all the core issues of the conflict are on the table, including the sensitive issue of settlements.
"In the interim, the limited construction under way will in no way impact upon the final contours of a peace agreement. Ultimately, it's not about settlements it's about reaching a historic peace settlement," he added.
An organisation representing Jewish settlers told the BBC they were not counting houses and the settlements needed to grow at a natural pace.
BBC News
