NEW YORK (REUTERS) - At least four emails from the private email account that former US Secretary of State Hillary Clinton used while in office contained classified information, according to a government inspector's letter that has deepened the email controversy dogging Clinton's 2016 presidential campaign.
The inspector general who oversees US intelligence agencies wrote in a letter to members of Congress on Thursday that a sampling of 40 of about 30,000 emails sent or received by Clinton found at least four that contained information the government had classified as secret.
The information was classified at the time the emails were sent, according to the inspector general, Charles McCullough.
"This classified information should never have been transmitted via an unclassified personal system," McCullough said in a joint statement on Friday, along with his equivalent at the State Department, Steve Linick.
The information remains classified to this day, the statement said.
The emails in question are not among those the State Department, which plans to eventually release as many as information laws allow, has already made public.
Clinton has said no classified information was contained in her emails, a large portion of which she handed over to the State Department last year.
It remains unclear if the classified information was included in emails sent by Clinton, or only in those received by her.
The inspectors general do not say whether they believe Clinton was aware the information was classified.
Clinton's use of her private email account linked to a server in her New York home for her work as America's top diplomat came to light in March and drew fire from political opponents who accused her of sidestepping transparency and record-keeping laws.
The frontrunner to represent the Democratic Party in the November 2016 election, Clinton has repeatedly said she broke no laws or rules by eschewing a standard government email account.
Clinton spokesman Nick Merrill did not respond to questions about the assertions made by the inspectors general. He has previously said the former first lady "followed appropriate practices in dealing with classified materials."
- Concern about server -
Even those who use an official government account for work cannot send classified information via email, State Department officials have said, but must use separate secure communication systems.
But the inspectors general said in their statement that their main concern was "to notify security officials that classified information may exist on at least one private server and thumb drive that are not in the government's possession."
This may encourage some of Clinton's Republican opponents, who have unsuccessfully tried to get Clinton to relinquish her private email server for inspection, to renew their efforts.
The US Justice Department said on Friday it had been notified of the concerns of the inspectors general and was weighing whether to look into the possible mishandling of classified information.
Clinton handed over some 30,000 emails from the private account to the State Department after she quit in 2013, but many thousands of others that she says are not related to her work were deleted.
Clinton did not directly address the statements made by the inspectors general on Friday. But at the start of a speech in New York, she deviated briefly from planned remarks about her economic platform to address the latest round of news reports about the email issue. "We are all accountable to the American people to get the facts right, and I will do my part," Clinton said.
McCullough said State Department officials told his office "that there are potentially hundreds of classified emails within the approximately 30,000 provided by former Secretary Clinton."
Republicans in Congress and on the presidential campaign trail have seized on the email scandal to portray Clinton as continuing secretive practices they say they also characterized President Bill Clinton's eight years in office.
While Clinton faces little competition for the Democratic Party's nomination, several recent polls have found a majority of voters find her untrustworthy, a perception exacerbated by controversy over her emails.