(J. Scott Applewhite/AP Photo)

Director of National Intelligence James Clapper apologized to Congress in a letter released today for giving a "clearly erroneous" answer to a question about whether the government collects data on millions of Americans.

"My response was clearly erroneous - for which I apologize," Clapper wrote in a letter to Senate Intelligence Committee Chairman Dianne Feinstein, D-Calif.

The letter came after Clapper was accused of lying in response to a question by Sen. Ron Wyden, D-Ore., about whether the National Security Agency collects "any type of data at all on millions or hundreds of millions of Americans."

In his March testimony, Clapper answered "no," later adding, "not wittingly."

It was later revealed that the NSA does collect "metadata" from telephone and Internet companies on millions of Americans - information that reveals information like the time, date and phone numbers of telephone calls, not the content of those calls.

"In light of Sen. Wyden's reference to 'dossiers' and faced with the challenge of trying to give an unclassified answer about our intelligence collection activities, many of which are classified, I simply didn't think of Section 215 of the Patriot Act," which allows the government to collect "business records" or metadata from telephone and Internet companies, Clapper said. "Instead, my answer addressed collection of the content of communications."

The explanation came after Clapper offered conflicting explanations on why he answered the way he did.

Wyden has said that his office not only gave Clapper a list of questions ahead of time, but also asked for a clarification from Clapper's office after his testimony.

In a statement today, a spokesman for Wyden said that a staff member in the Senator's office asked Clapper to correct the public record after the March hearing, which he "refused" to do.

"Senator Wyden had a staff member contact the Office of the Director of National Intelligence on a secure phone line soon after the March hearing to address the inaccurate statement regarding bulk collection on Americans," said Wyden spokesman Tom Caiazza. "The ODNI acknowledged that the statement was inaccurate but refused to correct the public record when given the opportunity. Senator Wyden's staff informed the ODNI that this was a serious concern."

"Senator Wyden is deeply troubled by a number of misleading statements senior officials have made about domestic surveillance in the past several years," he added.