The tweets were reportedly issued by hackers who, the network says, gained illegal access to FOX's "foxnewspolitics" account with the microblogging service.
According to the tweets, the president was shot this morning at a campaign event in Iowa, dying shortly after, and the assassin remained at large.
The series of messages began:
"BREAKING NEWS: President @BarackObama assassinated, 2 gunshot wounds have proved too much. It's a sad 4th for #america. #obamadead RIP"
"We wish @joebiden the best of luck as our new President of the United States. In such a time of madness, there's light at the end of tunnel"
The messages were visible until at least 11 a.m EDT, but have since been removed from the Twitter account.
The president is actually celebrating the 4th of July with military at a White House barbecue.
This isn't the first time the network had Twitter accounts hijacked. In January 2009, a hacker broke into FOX's "foxnews" account to transmit a message with slanderous intent about talk-show host Bill O'Reilly.
FOX News and its affiliates also made erroneous statements alluding to death of Obama earlier this year. Reporting the slaying of terrorist Osama bin Laden, a FOX anchor concluded the story by saying "President Obama is, in fact, dead." (See video of that broadcast by clicking here.) Many crawl text statements of or similar to "Obama dead" appeared on the network during the same time.
FOX News has been directly attributed as inspiration to violent actions in the country for at least three years. It and its newscasters have been credited as the impetus in the slaying of police officers and a minister, violence at a Town Hall meeting, the plotted assassination of a congresswoman, and an attempt to attack a business with weapons - and directly by those committing the crimes.
The network faces no legal repudiation for these and other errors, even if intentional. In a 2003 federal court case, FOX attorneys argued there is no law against knowingly distorting news reports with deliberate intentions to mislead. FOX News won the case.