Social networking site Facebook suffered from a widespread outage on Tuesday, before coming back online.
Millions of users were unable to access their accounts.
Users in some countries also had difficulties accessing photo-sharing app Instagram.
Facebook in the UK and Ireland said it was “aware that many people are currently having trouble accessing Facebook and Instagram”.
“We’re working to get things back to normal as quickly as possible,” a spokeswoman said.
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.”
The sites appear to have been unavailable for about 40 minutes before coming back online.
A hacker group called ‘Lizard Squad’ claimed responsibility for the outage, according to the BBC’s technology correspondent, Rory Cellan-Jones.
The group claimed to have attacked the website for Malaysia Airlines on Monday.
Source: BBC