Image copyright Reuters Image caption Hackers are thought to have obtained a scan of Michelle Obama's passport after hacking an email account

The White House says it is investigating a "cyber breach" after what appeared to be a scan of Michelle Obama's passport was published online.

The scan appeared to have been taken from a Gmail account belonging to a White House employee, a spokesman said.

Other confidential information was published online, including travel details, names, social security numbers and birth dates of members of staff.

The White House said it had not yet verified the documents.

DCLeaks.com, a hacker group which last week published personal emails from an account belonging to former US Secretary of State Colin Powell's emails, claimed responsibility for the hack.

The US attorney general, Loretta Lynch, said the incident was "something that we are looking into". White House press secretary Josh Earnest said the breach "should be a wake-up call for all of us".

Mr Earnest said that the employee targeted by the hackers was a contract worker and not a permanent member of staff.

He said: "At this point I cannot announce any sort of conclusion that's been reached about the individual or individuals that may have been responsible for the cyber breach that resulted in this information being leaked."

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The Secret Service, which is responsible for protecting the President and First Lady, said it was "concerned" about the apparent hacking.

"The Secret Service is concerned any time unauthorised information that might pertain to one of the individuals we protect, or our operations, is allegedly disclosed," said communications director Cathy Milhoan.

In July, hackers released a string of emails from the Democratic National Committee (DNC), prompting the resignation of chairwoman Debbie Wasserman Schultz. State-sponsored Russian hackers have been accused of behind the DNC leaks.

And on Friday, internet giant Yahoo confirmed that hackers stole information from about 500 million users in 2014, in what appears to be the largest publicly disclosed cyber-breach in history.