Facebook said its systems were coming back after it fixed problems that caused more than 21 hours of outages for users around the globe, according to a tweet early Thursday afternoon.
The social networking site blamed its latest difficulties on a server.
"Yesterday, as a result of a server configuration change, many people had trouble accessing our apps and services," the tweet, posted just before 12:30 p.m., said. "We've now resolved the issues and our systems are recovering."
The social networking site's outage, which also hit Instagram and Messenger users, was one of Facebook's longest and deepest, experts said, depriving individuals from contacting one another and forcing businesses to seek workarounds.
Facebook's reputation has suffered a series of blows in the past several months, from concerns about sharing users' data without their consent to intensified scrutiny from antitrust overseers.
Twitter, the platform Facebook used to announce the service restoration, is one of its rivals.
"We’re very sorry for the inconvenience and appreciate everyone’s patience," Facebook said.
The outage began around midday on Wednesday. That afternoon Facebook, based in Menlo Park, California, informed its users via Twitter: "We're focused on working to resolve the issue as soon as possible, but can confirm that the issue is not related to a DDoS attack."
The acronym DDoS stands for "Distributed Denial of Service," when hackers overwhelm a site.
Areas with the most outages on Thursday in the early afternoon, according to the monitoring service for developers, Downdetector.com, included parts of the North America, from Vancouver to Los Angeles and San Diego to Atlanta, Toronto and New York.
London and Paris also were highlighted on the Downdector outage map, and while the problems appeared to have been resolved in Tokyo, Manila remained a hot spot. So did areas of Peru, Brazil and Uruguay.
Facebook was pilloried for the difficulties on social media sites, including Twitter, and comments detailing complaints poured into Downdetector.com, though its graphs showed complaints had fallen markedly by 7 a.m. Thursday and remained low in the early afternoon.
Still, Downdector.com's comment section included many complaints from users around the nation, still reporting problems after Facebook announced service was returning.