Hackers from the online group Lizard Squad have claimed responsibility for the attack, which took the two social media sites down at around 6am GMT.

Both sites, which have a total of 1.5billion users, appeared with error messages in the United States, Europe and Asia for around an hour.

But despite hackers claiming they took the social media giants offline, Mark Zuckerberg's Facebook, which also owns Instagram, refused to say what the fault was.

The social media blackout also affected the dating mobile app Tinder, as well as AOL Instant Messenger and Hipchat. 

While it was down Facebook said they were 'aware' of trouble accessing the site and added: 'We're working to get things back to normal as quickly as possible.'

An Instagram spokesman posted on Twitter: 'We're aware of an outage affecting Instagram and are working on a fix. Thank you for your patience.' 

There is no word at this time what is causing the outage, and whether or not it might have anything to do with the ongoing blizzard, which is expected to dump 36 inches of snow in parts of New York, Massachusetts, Rhode Island, New Jersey and Connecticut, where key servers are based.

The headquarters of Facebook are located in Menlo Park, California - an area which has not been affected by the storm.

The hashtag #facebookdown immediately started tending on Twitter, which remains operational. 

Facebook had 1.25 billion monthly active users at the end of September last year, while photo-sharing service Instagram has 300 million active monthly users uploading around 70 million photos per day.

The Lizard Squad is a group of hackers that has caused havoc in the online world before, taking credit for attacks that took down the Sony PlayStation Network and Microsoft's Xbox Live network last month.

In August, it also tweeted to American Airlines that there might be explosives on a plane carrying the president of Sony Online Entertainment, which makes video games, forcing the flight to be diverted.

Yesterday, it claimed to have targeted The Malaysia Airlines website, leaving a message saying '404 Plane Not Found' and declaring it part of their 'cyber caliphate'

Users logging on to the site of Malaysia's national carrier earlier today were greeted with the picture of a lizard in a top hat, monocle and tuxedo, smoking a pipe.

The image was surrounded by the message '404 Plane Not Found', an apparent reference to the airlines' unexplained loss of flight MH370 last year with 239 people aboard.

The extent of any links with the Islamic State, however, are not yet known.

The jihadist group has seized large swathes of Syria and Iraq in a brutal campaign and declared an independent Islamic 'caliphate'.

It also has used social media to recruit and spread its message.

(dailymail.co.uk)