Iran’s political turmoil has prompted a growing number of the country’s officials to defect or leak information to the West, creating a new flow of intelligence about its secretive nuclear program, U.S. officials said.

The gains have complicated work on a long-awaited assessment of Iran’s nuclear activities, a report that will represent the combined judgment of more than a dozen U.S. spy agencies. The National Intelligence Estimate was due last fall but has been delayed at least twice amid efforts to incorporate information from sources who are still being vetted.

Director of National Intelligence Dennis Blair said in a brief interview last week that the delay in the completion of the NIE “has to do with the information coming in and the pace of developments.”

Some of the most significant new material has come from informants, including scientists and others with access to Iran’s military programs, who are motivated by antipathy toward the government and its suppression of the opposition movement after a disputed presidential election in June, according to current and former officials in the United States and Europe who spoke on the condition of anonymity to discuss the intelligence gains.

“There is a wealth of information-sharing going on, and it reflects enormous discontent among Iranian technocrats,” said a former U.S. government official who until recently was privy to classified reports about intelligence-gathering inside Iran. “Among senior technocrats, whether in the nuclear program or older technical fields or even banking, the morale is very low.”

In recent weeks, U.S. officials have acknowledged that an Iranian nuclear scientist defected to the West in June. Shahram Amiri, 32, vanished while on a religious pilgrimage in Saudi Arabia and has provided spy agencies with details about sensitive programs, including a long-hidden uranium-enrichment plant near the city of Qom, intelligence officials and Europe-based diplomats said.

Sources said there has been a spate of other recent defections by diplomatic and military officials, some of which have not been made public. Among the defectors was a top diplomat at the Iranian mission in Oslo, who said he was pressured to falsify election returns for Iranian nationals who had cast votes at the embassy.

The revisions to the NIE underscore the pressure on the U.S. intelligence community to produce an accurate assessment of Iran’s nuclear ambitions as President Barack Obama pursues a policy aimed at preventing the country from acquiring an atomic bomb. The community’s 2007 assessment presented the startling conclusion that Iran had halted its work on developing a nuclear warhead, provoking enduring criticism that the report had underestimated the Iranian threat.

Officials briefed on the new version, which is technically being called a “memo to holders” of the first, say it will take a harder tone. One official who has seen a draft said that the study asserts that Iran is making steady progress toward nuclear weapons capability but that it stops short of concluding that the Islamic republic’s top leaders have decided to build and test a nuclear device. Iran says its nuclear program is entirely peaceful.

The departures of Amiri and others have given new momentum to a “brain drain” program set up by the CIA in recent years as part of a broader effort to slow Iran’s nuclear progress by sabotaging equipment being shipped into the country and enticing key scientists to defect.