Facebook is blaming tinkering under the bonnet for a global outage earlier today, which also took out the Facebook-owned Instagram and Whatsapp.
"Earlier today, a configuration change caused Facebook services to be unavailable to some people," a Facebook spokesman said.
"We quickly investigated and resolved the issue. We apologise for any inconvenience."
There was no immediate elaboration on what features the configuration change applied to.
This morning, Facebook services dropped for the second time in three weeks.
Down Detector, a service that keeps track of website performance, recorded a major spike in reports of an interruption to Facebook services this morning.
The outages appeared to be affecting all three services on a global scale, with Facebook and Instagram's websites down, and apps working intermittently.
"We're sorry, but something went wrong. Please try again," said the Instagram app when users tried to access any part of it earlier this morning. Its feed is now refreshing but the messaging function is still out.
WhatsApp displayed a 'Connecting' message and circular icon near the top, with the Facebook Messenger app displaying a similar error. Some messages from both services are getting through, but after delays of up to half an hour.
Meanwhile, some Facebook app users saw a sign-in prompt, despite already being logged in.
Facebook also experienced technical difficulties at the end of last month.
Those issues were, however, restricted to the photo-sharing app Instagram.
The latest outage had a much wider impact, affecting Facebook, Instagram, ad services and a number of other properties within the Facebook group.
Given the expense involved, Facebook usually moves to rectify these issues rapidly.
The platform's performance remains intermittent, with many still reporting issues globally.
On April 4, data from more than 500 million Facebook accounts was found available on a website for hackers.
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