Users of PCs and Facebook's mobile app reported they lost access in Asia, Canada, the United States, Australia and the U.K. Facebook-owned Instagram was also inaccessible.
Facebook said the disruption was caused by a technical change and wasn't a cyberattack. "This was not the result of a third party attack but instead occurred after we introduced a change that affected our configuration systems," its statement said.
The temporary loss of service may be Facebook's biggest outage since Sept. 24, 2010, when it was down for about 2.5 hours.
On its website for developers, Facebook said the "major outage" lasted one hour.
The outage occurred at midday in Asia, and after Facebook was restored, some users reported that the site was loading slowly or not functioning fully.
Lizard Squad, a group notorious for attention-seeking antics online, claimed responsibility on Twitter for the outages.
Guillermo Lafuente, security consultant at MWR InfoSecurity, said a technical fault was more plausible. A denial-of-service attack would have made the sites unreachable rather than accessible with an error message displayed, he said. Facebook's use of multiple data centres also meant an attack on one would have affected one region, while this outage was worldwide.
Also, restoring service would be a matter of reversing the technical changes, which matched with the brevity of the outage, LaFuente said.
Facebook has about 1.35 billion active users and Instagram has some 300 million. The outage came a day ahead of Facebook reporting its quarterly earnings.
Lizard Squad on Monday claimed it had defaced the Malaysia Airlines website and would release data from the airline. Its previous hacking claims have been mostly aimed at gaming or media companies.