The US Secret Service has launched an investigation after hackers posted on the Fox News Twitter account that president Barack Obama was dead.
The hackers wrote six tweets, reporting that Mr Obama had been shot to death in Iowa and the gunman had not been apprehended.
The messages remained online for more than two hours before they were taken down.
Fox News says the tweets were "malicious" and "false" and says it will conduct an investigation of its own.
"We will be requesting a detailed investigation from Twitter about how this occurred, and measures to prevent future unauthorised access into FoxNews.com accounts," Fox News Digital vice-president and general manager Jeff Misenti said.
"Those reports are incorrect, of course, and the president is spending the July 4 holiday with his family," Fox News said.
The White House declined to comment but the Secret Service, which is charged with protecting the president, said it was looking into the incident.
"The Secret Service is investigating the matter and will conduct the appropriate follow-up," spokesman George Ogilvie said.
The first hacked tweet appeared around 2am (local time) and said: "@BarackObama has just passed. The President is dead. A sad 4th of July, indeed. President Barack Obama is dead."
The next one, "@BarackObama has just passed. Nearly 45 minutes ago, he was shot twice in the lower pelvic area and in the neck; shooter unknown. Bled out."
Cortesía: ABC News