Israeli intelligence officials now estimate that Iran won’t be able to build a nuclear weapon before 2015 or 2016, pushing back by several years previous assessments of Iran’s nuclear ambitions.

Intelligence briefings given to McClatchy over the last two months have confirmed that various officials across Israel’s military and political echelons now think it’s unrealistic that Iran could develop a nuclear weapons arsenal before 2015. Others pushed the date back even further, to the winter of 2016.

“Previous assessments were built on a set of data that has since shifted,” said one Israeli intelligence officer, who spoke to McClatchy only on the condition that he not be identified. He said that in addition to a series of “mishaps” that interrupted work at Iran’s nuclear facilities, Iranian officials appeared to have slowed the program on their own.