'President Barack Obama is Dead'

"We will be requesting a detailed investigation from Twitter about how this occurred, and measures to prevent future unauthorized access into FoxNews.com accounts," Misenti said.

Cyber breaches

A group calling itself The ScriptKiddies claimed responsibility for sending the tweets - including "#ObamaDead, it's a sad 4th of July" - from the "foxnewspolitics" news feed before Twitter suspended its access.

In all, six false tweets were issued, saying Obama had been shot at a restaurant in Iowa while campaigning. Obama was not in Iowa this weekend. He returned on Sunday to the White House from a brief trip to Camp David in neighbouring Maryland.

The Foxnews.com account hacking followsa wave of highly publicised cyber security breaches, including attacks on the bank Citigroup, Sony, Apple and the US Senate and Brazilian presidential websites.

Monday's breach raised questions about the integrity of news feeds on Twitter, which is increasingly used by news outlets as well as government officials as a way to reach readers and supporters.

Twitter spokeswoman Jodi Olson declined to say whether the company would add more security as a result of the attack, but stressed it was important for users to shield their profiles.

"We don't comment on specific accounts. In general, though, it's always good to remind people of the importance of actively protecting their account credentials," Olson said, recommending that all users have a strong password as a "starting point."

The FoxNews.com hacking came two days before Obama's first "Twitter town hall" where he will field tweeted questions about the economy and jobs.

Twitter's co-founder and executive chairman Jack Dorsey is due to moderate that Wednesday session at the White House. Fox.com, another Fox Entertainment Group website, was the target of an attack by hacker group Lulz Security in May.

LulzSec has also made assaults on Sony, the US Central Intelligence Agency (CIA) and other targets. The attacks have mostly resulted in temporary disruptions to websites and the release of user credentials.