By Lesley Wroughton
WASHINGTON (Reuters) - Hillary Clinton did not hand over at least 15 emails from her time as secretary of state, the U.S. State Department said on Thursday, undercutting her claim that the 30,000 work emails she provided from her personal server were a complete record.
The department learned the email record was apparently incomplete after Sidney Blumenthal, an old friend and informal adviser to Clinton, provided several previously undisclosed emails to U.S. lawmakers investigating the deadly 2012 attack on diplomatic staff in Benghazi, Libya.
The 15 emails were either missing from the records Clinton provided or included only in partial form. The department said they were not relevant to the attacks on Benghazi although copies posted online showed that they discussed the turmoil in Libya more generally.
Clinton spokesman Nick Merrill said in an email on Thursday that the Democratic presidential candidate had given the department "all emails in her possession from Mr. Blumenthal."
He said he could not explain the origins of the additional correspondence Blumenthal provided in response to the lawmakers' subpoena.
Clinton, the favorite to become her party's nominee for the 2016 presidential election, has weathered criticism that she side-stepped record-keeping and transparency rules by using only a private email account for her work. The private address was connected to a server in her home.
The arrangement was made public in March, more than two years after she stepped down as the top U.S. diplomat. Clinton said she used the private email account for the sake of convenience and broke no rules.
Recent polls show more than half of all voters say she is not trustworthy, in part because of her email habits, although this has not put a deep dent in her popularity among Democrats.
Trey Gowdy, the Republican congressman in charge of the select committee investigating the Benghazi attack, said Clinton's incomplete email record "raises serious questions".
"This has implications far beyond Libya, Benghazi and our committee's work," Gowdy said in a statement. "This conclusively shows her email arrangement with herself, which was then vetted by her own lawyers, has resulted in an incomplete public record."
In March, Clinton said in an impromptu news conference at the United Nations headquarters that she gave the State Department all emails she sent and received that "could possibly be work-related".
She said the 30,490 emails she handed over in December after the State Department asked for her records included all that referred to Libya or Benghazi, as well as all work-related correspondence from what her office described as "long-time friends".
She said that once those copies were made, all her emails, including another 30,000 or so that were deemed personal, were deleted from the server.
Clinton spokesman Merrill declined to respond when asked whether some emails might have been deleted at an earlier date, before the State Department made its request.