Secret Service spokesman George Ogilvie says the law enforcement agency whose job it is to protect the president will conduct a probe of the false postings and that "we will conduct the appropriate follow up."
Hackers broke into the FoxNewsPolitics account early Monday, leaving a series of six tweets reporting that Obama had been shot to death in Iowa and the shooter was unknown.
In a statement posted on its website, Fox News called the tweets "malicious" and "false."
"We will be requesting a detailed investigation from Twitter about how this occurred, and measures to prevent future unauthorized access into FoxNews.com accounts," said Jeff Misenti, vice president and general manager of Fox News Digital.
An online magazine at New York's Stony Brook University, Think, reported that initial posts around midnight indicated the Fox News Twitter account had been hacked by a group called the Script Kiddies. Harmless posts announcing the group's hacking of the Fox News account were followed by the false posts about Obama, according to Think.
A Think staffer, Adam Peck, wrote on the magazine's website that he had exchanged electronic messages with a person claiming to be with the Script Kiddies shortly after the initial hacking. Later, however, the unidentified person would not confirm that the group was behind the Obama posts, Peck wrote.
Obama spent the Independence Day holiday at a barbecue at the White House with military families and administration staffers.
Fox's political Twitter account has more than 34,000 followers. Fox News did not immediately respond to a request for comment.