The emails may be withheld until after Obama leaves office under the Presidential Records Act, according to the White House, a law that governs public access to the president`s records.

The number of emails involved has not been made public. The White House said Obama and Clinton, who is now running as a Democrat to succeed him in office in 2017, exchanged emails "on occasion."

A federal judge has ordered the State Department to publicly release all of Clinton`s emails from her four years as the nation`s top diplomat between 2009 and 2013 after a Vice News reporter sued the department under freedom of information laws.

The State Department is releasing them in monthly batches through to next January; another 4,400 were released on Friday. They range from dull exchanges on scheduling matters to information that the government has redacted from public release because it is classified and could harm national security if disclosed.

It was not immediately clear whether U.S. District Judge Emmet Sullivan would agree with the U.S. executive branch`s decision, which was first reported by the New York Times, that Clinton`s emails with Obama did not have to be released under his order. The State Department declined to comment.

Steven Aftergood, the director of the Federation of American Scientists` Project on Government Secrecy, said that "email messages to the president are potentially exempt" from release under freedom of information laws. However, federal judges have occasionally ruled against this exemption, Aftergood said.

Ryan James, a lawyer representing Vice News in the Clinton email lawsuit before Judge Sullivan, said he planned to challenge every "withholding or redaction" that does not meet the standards of freedom of information laws.

Clinton has spent months defending her decision to use only a private email account connected to a server in her New York home for her work as secretary of state, an arrangement that first came to light in March. She returned the emails to the department late last year.

Although she remains the favorite to become the nominee among Democratic voters, more than half of Americans have said in a series of recent opinion polls that they find her untrustworthy, in part because of her email habits.

Her critics say the set-up was an attempt to skirt transparency laws and may have made classified information vulnerable to hackers, charges she denies.

The Federal Bureau of Investigation has taken the server Clinton used while secretary of state, along with other computer hardware belonging to her, to examine whether sensitive government information was mishandled, which can be a crime in some circumstances, or exposed.

Clinton has said she did not knowingly send or receive classified information through her private email system, a practice the government forbids.

But hundreds of emails that have been made public so far contain information that is classified, according to the State Department. The department says it does not know how much of that information, if any, was classified at the time she sent or received it.

Another 270 or so emails released on Friday contain classified information, according to the State Department. At least a couple of those email exchanges include classified information about military plans or weapons systems.

Much of the classified material in her emails is information provided in confidence by foreign governments. Government regulations say this sort of information must be classified, and Clinton has declined to explain why she and her staff often did not treat it as such.

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