Millions of users were unable to access their accounts.Users in some countries also had difficulties accessing photo-sharing app Instagram.
Facebook said it believed its own engineers had caused the problem, downplaying claims that a hacking group had been responsible.
“Earlier this evening many people had trouble accessing Facebook and Instagram,” a spokeswoman told the media.
“This was not the result of a third-party attack but instead occurred after we introduced a change that affected our configuration systems.We moved quickly to fix the problem, and both services are back to 100% for everyone.”
The sites appeared to have been unavailable for about 40 minutes before coming back online.