The Secret Service is to investigate the hacking of Fox News's political Twitter account over updates claiming that President Barack Obama had been assassinated.
Secret Service spokesman George Ogilvie said the law enforcement agency, whose job it is to protect the president, will conduct an investigation of the false postings.
A series of six tweets coming from the FoxNewsPolitics account reported that Mr Obama had been shot dead in Iowa and the gunman was unknown.
In a statement posted on its website later, Fox News called the tweets "malicious" and "false". It said the hacking was being investigated.
Mr Obama plans to spend the July Fourth US Independence Day holiday at a barbecue at the White House with military families and administration staff.
Fox's political Twitter account has more than 34,000 followers.