Obama was "shot twice at a Ross' restaurant in Iowa while campaigning. RIP Obama, best regards to the Obama family," read one of several Twitter messages posted on @FoxNewsPolitics early Monday.
"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 last in the series of tweets said later.
An article on FoxNews.com confirmed the hack.
"Hackers sent out several malicious and false tweets claiming that President Obama had been assassinated," it said. "Those reports are incorrect, of course, and the president is spending the July 4 holiday with his family.
"The hacking is being investigated, and FoxNews.com regrets any distress the false tweets may have created."
One of the false message said, "it's a sad 4th of July ... The shooter will be found." That message encouraged Twitter users to post the message on their own Twitter accounts, which would spread the fake news. Several users did just that.
The tweets generated headlines around the world, criticisms and mockery on Twitter, with firebrand liberal TV host Keith Olbermann frantically tweeting to many individual Twitter users that Obama is fine. He asked Twitter users not to re-post the messages.
The first of the false tweets were posted around 2 a.m. ET. They were still up six hours later, with no explanation of their origin. The Twitter messages asserting that Obama had been attacked came after a message that said, "Just regained full access to our Twitter and email. Happy 4th."
The @FoxNewsPolitics Twitter account has 34,566 followers.
Twitter did not immediately responded to CNN requests for comment.