Facebook briefly suffered an international outage early Thursday, leaving millions of users with an error message.
"We're working on getting this fixed as soon as we can," a statement on the social networking site said.
The outage appeared to stretch across the globe: users in the United Kingdom, Israel and India were among those affected.
Within minutes, the hashtag "WhenFacebookWasDown" was trending globally on rival social-networking site Twitter.
In under an hour, the social networking site started to come back online for some users and Facebook apologized for the inconvenience in a statement.
"We experienced an issue that prevented people from posting to Facebook for a brief period of time," the company said. "We resolved the issue quickly, and we are now back to 100%."
A Facebook spokesman would not specify how many users were affected or elaborate on what caused the problem.
Facebook claims nearly 1.28 billion users across the world. It counts more than 80 percent of its users outside the U.S. and Canada.