Washington (CNN) -- A prominent Republican senator called Wednesday for a top Justice Department figure to resign, saying Assistant Attorney General Lanny Breuer was dishonest with Congress about his knowledge of the gun-running Operation Fast and Furious.
Sen. Charles Grassley, an Iowa conservative, said Breuer misled Congress about his awareness of a February 4 letter that denied any gun-running operation existed.
The Justice Department recently withdrew the letter due to inaccurate information, and Grassley said Wednesday that e-mails turned over to congressional investigators showed Breuer saw various versions of the letter -- including the final one submitted to Congress -- before it was sent in February.
In addition, Grassley said Breuer knew in 2010 of a previous gun-running operation by the Bureau of Alcohol, Tobacco, Firearms and Explosives in the Bush administration, but failed to notify superiors or Congress about it.
"Mr. Breuer's failure to be candid and forthcoming before this body irreparably harms his credibility," Grassley said, later adding: "Mr. Breuer has lost my confidence in his ability to effectively serve the Justice Department. If you can't be straight with the Congress you don't need to be running the criminal division. It is time to stop spinning and start taking responsibility."
In response, Justice Department spokeswoman Tracy Schmaler said Breuer "has acknowledged his mistake in not making -- and therefore not alerting department leadership to -- a connection between the allegations made about Operation Fast and Furious and the unacceptable tactics used years earlier."
Attorney General Eric Holder "continues to have confidence" in Breuer's ability to lead the department's criminal division, Schmaler said.
Holder is scheduled to appear Thursday before a House committee investigating possible wrongdoing in Operation Fast and Furious.
Breuer and Holder previously apologized to a Senate committee and to Grassley in particular about the false information in the February letter. Both have insisted they did not know the assertions were wrong when the department sent Grassley the letter.
However, Grassley said Wednesday that the additional documents recently provided to congressional investigators show that Breuer should have been aware that the letter contained false assertions, due to his knowledge of a similar previous program called Operation Wide Receiver.
Operation Fast and Furious began in 2009 and allowed illegally purchased firearms to be taken from gun stores in Arizona across the border to drug cartels. The intent of the operation was to monitor the flow of weapons to their ultimate destination.
However, hundreds of weapons were lost or unaccounted for, and a storm of outrage erupted when two of the missing weapons were found at the site where Border Patrol agent Brian Terry was killed in December.
CNN's Tom Cohen, Terry Frieden and Jim Barnett contributed to this report.