Facebook, the world's largest social network, and its Instagram photo-sharing site, suffered temporary outages around the world for up to an hour on Tuesday and the company said later that an internal software networking error was to blame.
The outage at Facebook appeared to spill over and temporarily slow or block traffic to other major Internet sites, according to web and mobile user reports from around the globe.
A hacker group associated with other recent high-profile attacks sought to take credit for the outages, but Facebook denied in a statement that any outside party was responsible.
"This was not the result of a third-party attack but instead occurred after we introduced a change that affected our configuration systems," the Facebook statement said. "Both services are back to 100 percent for everyone."
Users in the United States and many countries in Asia and Europe reported that they were unable to log on to the websites of Facebook, Instagram and corresponding mobile apps including Facebook and Facebook Messenger from around 0600 GMT. Services were restored within an hour of going down, users reported.
During the outages, Facebook users were greeted with the message: "Sorry, something went wrong. We're working on it and we'll get it fixed as soon as we can."
A Twitter account that purports to speak for hacker group "Lizard Squad" posted messages suggesting that it was behind an attack that temporarily blocked several major web sites, including Facebook and Instagram.
The Lizard Squad is a group of unknown hackers that has taken credit for several high-profile outages, including the attacks that took down the Sony PlayStation Network and Microsoft's Xbox Live network last month.