The US Secret Service said it was investigating the apparent hacking of an official Twitter account operated by Fox News that posted a series of tweets claiming President Barack Obama had been assassinated.

The Twitter feed for the television network's political news -- @FoxNewspolitics -- sent out a series of "malicious and false tweets," starting around 2:00 am, Fox News confirmed in a statement. The posts had not been taken down hours later.

"@BarackObama has just passed. The president is dead. A sad 4th of July, indeed. President Barack Obama is dead," read the first of the Obama-related tweets.

Just before false posts began, the hackers apparently announced their control to the account, with the post: "Just regained full access to our Twitter and email. Happy 4th."

The updates, which were "retweeted" by thousands on the micro-blogging site and prompted headlines around the world, said Obama had been "shot twice at a Ross' restaurant in Iowa" during a campaign spot.

The US leader was in fact in Washington, not Iowa, and was planning to celebrate the July 4 holiday with his family and military families later Monday.

"President @BarackObama assassinated, 2 gunshot wounds have proved too much. It's a sad 4th for #america. #obamadead RIP," continued the tweets.

Fox News said the hacking was being investigated, and that it "regrets any distress the false tweets may have created."

Asked about the apparent hacking, Edwin Donovan, a spokesman for the Secret Service -- the federal law enforcement agency tasked with ensuring the president's safety -- was looking into the fake posts.