"The whole concept is really flawed," said Leverett, a long-time critic of U.S. Iran policy. "It's almost structurally designed to make sure we get skewed information."

The Iran watchers' observations generally appear above the signature of other embassy officials, though their identities do not seem to be a secret; Assistant Secretary of State Jeffrey Feltman named several, offering specific praise for their work, in a cable that was labeled unclassified. Nevertheless, at the State Department's request, McClatchy deleted their names on the version of the cable that it posted on its website.

As for the people the Iran watchers talked to, McClatchy also withheld the names of many — as well as other information that might help identify them — to protect them from possible retribution.

Of course, the Iran watchers are not the only source of information for the U.S. government, which trades information with its allies, most of whom do maintain a diplomatic presence in Tehran, and presumably spies on the country through more covert means.

Even so, the cables show, the U.S. often has a difficult time knowing what is going on there.

The largest mass protests in the Islamic republic's history "were unanticipated by most of us," Feltman acknowledged to the Iran watchers on June 26, 2009, two weeks after disputed presidential elections sparked massive demonstrations and rioting in a challenge to Iran's theocracy.

"Without a post in Iran and given the Iranian government crackdown on its citizens, journalists, foreign diplomats and most modes of communication, our ability to get reliable news and make sense of the situation here in Washington has proved most difficult," Feltman wrote.

The Iran watchers themselves are aware of the vulnerabilities of their information.

In the conclusion of the cable that recounted the alleged plot to seize Saudi Arabia's embassy in Iran, the cable's author notes that the source of the anecdote is citing someone with access to Iran's Supreme National Security Council. But the cable writer offers no assessment of the story's accuracy.

"What can be said in this cable is that the purported original source of most of the above information is credibly in a position to have access to the information provided," the cable said. "However, while our strong impression is that the Baku contact genuinely believes his information is accurate, we cannot yet assess the credibility of the information itself."

Other cables show more direct knowledge.

In one, an American diplomat recounts how former Iranian president Mohammad Khatami, who was planning to seek his old office in 2009, asked for U.S. government help in arranging a meeting with the Swiss ambassador to Tehran. The Feb. 24, 2009, cable said the reformist Khatami hoped the meeting would "highlight his international appeal" and circumvent regime curbs on his campaign websites.

In another 2009 cable, a diplomat tells how the Iraqi government had shared the passport information of Iranian diplomats in Baghdad and those applying for duty there with the United States so the U.S. government could determine which were Iranian intelligence officers or members of Iran's Islamic Revolution Guard Corps.