CIA officials questioned in the run-up to the Iraq War in 2003 whether key intelligence cited by President George W. Bush’s administration as a reason for a military invasion was faulty, according to a newly declassified CIA letter released Thursday by the chairman of the Senate Armed Services Committee.

The letter was sent March 13 of this year from CIA Director John Brennan to Sen. Carl Levin, the outgoing committee chairman, and introduced on the Senate floor on Thursday. Brennan confirmed that CIA field operatives “expressed significant concern” whether Muhammad Atta, one of the airliner hijackers in the Sept. 11, 2001, terrorist attacks, could have met with a former Iraqi intelligence officer, Ahmad Khalil Ibrahim Samir al-Ani, in Prague about five months earlier.

The so-called “Prague connection” was used by the Bush administration as a way of tying the 9/11 attacks to Iraqi President Saddam Hussein. The intelligence has been questioned for years, but the new CIA letter raises anew questions about why the Bush administration took the United States into the Iraq War despite concerns repeatedly being raised by U.S. intelligence officers about whether there was a tie between 9/11 and the Iraqi government.

On March 13, 2003 — less than a week before the U.S. invasion — CIA headquarters received a report from field operatives that questioned whether the “single-source” report about Atta being in Prague could have been true, the new letter by Brennan says.

“In particular, the field noted that while it remained possible that a meeting between Atta and al-Ani took place, investigative records subsequently placed Atta in the United States just before and just after the date on which the single-source report said the meeting was to have occurred, making it unlikely that Atta was in Prague at the time of the alleged meeting,” Brennan wrote.

“The field also warned that both the FBI and CIA had previously told foreign intelligence officials that they observed the ‘identifications’ like the one that was made by the source of the earlier report, during a period of high emotion four months after the September 11 attacks, could be faulty and would require further evidence,” the letter continues. “The field added that, to its knowledge, ‘there is not one [U.S. government counterterrorism] or FBI expert that… has said they have evidence or ‘know’ that [Atta] was indeed [in Prague]. In fact, the analysis has been quite the opposite.”

Brennan said in the new letter that he shared the information at Levin’s request because Americans deserve as full of an understanding as feasible about historical events.

Levin called Thursday for the full declassification of the CIA cable Brennan referenced.

“Earlier this year, Director Brennan wrote to me, refusing, as did his predecessors, to fully declassify the CIA cable,” Levin said. “But in his letter to me he makes public for the first time a few lines from that document. While this is a significant addition to the public record, and I will discuss that in a moment, it is still not the full cable, and I am calling on him to declassify and release the full cable.”

Levin said that Vice President Cheney and others knew that CIA officials questioned whether the Prague meeting could have occurred, but used it as justification for the war, anyway.

“The March 13, 2003, cable is an invaluable record in helping the American people understand how their elected officials conducted themselves in going to war,” Levin said Thursday. “Continuing to cloak this document with a veil of secrecy, revealing a few sentences at a time, allows those who misled the American people to continue escaping the full verdict of history. It deprives the American people of a complete understanding of how we came to invade Iraq.”