IRBIL, Iraq — U.S. Defense Secretary Ash Carter acknowledged on Thursday he sometimes used a personal, unsecured email account to conduct official business after he took office in February, a practice he called "entirely my mistake."
His admission followed a New York Times report revealing that he continued the practice even after Hillary Clinton triggered a wave of criticism in March for using a private email account to conduct government business while she was secretary of state. The FBI and several congressional committees are investigating Clinton.
Presidential chief of staff Denis McDonough found out in May about Carter's emailing and, through White House counsel, expressed concern to Pentagon lawyers, White House spokesman Josh Earnest said. Carter nonetheless persisted, telling reporters Thursday that he ended the practice "a few months ago."
Carter said he did not use his phone for classified information. The Defense Department said all his messages, which appeared to be largely about meetings and speeches, were backed up for record keeping on the department's email system.
Earnest made clear that Carter had erred in his email practices, but he said the consequences did not seem significant. He said the Pentagon had expressed willingness to cooperate with congressional inquiries.
Carter did not respond directly when asked by a reporter whether he had stopped using his personal account only after the Times filed a Freedom of Information request in September for some of his emails. He repeated that he had stopped "a few months ago. And basically, what that means is I was doing it for longer than I should have."
"I should have known better," Carter said while visiting Irbil, Iraq, where U.S. troops are training and advising Kurdish forces. "It's not like I didn't have the opportunity to understand what the right thing to do was. I didn't do the right thing."
"It's entirely my mistake. Entirely on me."
Clinton, now the front-runner for the Democratic presidential nomination, used her private account exclusively during her four years as the nation's top diplomat. Unlike Carter, Clinton also used her own private server set up in her home. Carter used an iPhone.
He told reporters that when he joined President Barack Obama's Cabinet in February, he was instructed in email security. He also has made cybersecurity one of his top policy priorities at the Pentagon, which is among the most frequently and intensively targeted government agencies by international hackers. An incursion last summer caused the Pentagon to shut down for weeks an unclassified email system used by senior officials.
In Washington, Sen. John McCain, R-Ariz., chairman of the Senate Armed Services Committee, said that in light of the attention given to Clinton's email use, it was "hard to believe that Secretary Carter would exercise the same error in judgment."
McCain said the committee has requested copies of the emails and will conduct a review "to ensure sensitive information was not compromised."
Rep. Mac Thornberry, McCain's counterpart in the House, said Carter should ask the Defense Department's inspector general to verify that no classified material was transmitted over unsecured channels by Carter or Deputy Defense Secretary Robert Work.
Jeremy Bash, who was chief of staff for Leon Panetta during Panetta's tenure at the CIA and while he was defense secretary from July 2011 to February 2013, said Panetta did his official work on a yellow legal pad and never used email.
"Like Secretaries Panetta and Hagel before him, Secretary Carter is trying to protect America from terrorists, weapons proliferators, and cyberattacks. I don't think anyone is going to care much about email practices," Bash said via email.
Senior administration officials, speaking on condition of anonymity to describe internal discussions, said McDonough had asked the White House legal team to raise the issue quickly with Pentagon senior staff in May and ensure that Carter's email was being managed appropriately.
Carter's press secretary, Peter Cook, declined to say whether Carter's practice had been a violation of Pentagon email policies.
The Times reported it had obtained 72 work-related emails that Carter sent or received from his personal email account.
Cook said in a statement issued after the Times published its account late Wednesday that Carter "stopped such use of his personal email and further limited his use of email altogether." The Times said the emails were exchanges between Carter and Eric Fanning, who was his chief of staff at the time and is now the acting Army secretary.
The emails were on a variety of work-related topics, the Times said, including speeches, meetings and news media appearances. In one such email, Carter discussed how he had mistakenly placed a note card in a "burn bag," the Times reported. Such bags are typically used to destroy classified documents.
Cook said Carter "does not use his personal email or official email for classified material. The secretary has a secure communications team that handles his classified information and provides it to him as necessary."
Burns reported from Washington. Associated Press writer Kathleen Hennessey in Washington contributed to this report.