New Delhi, Jan 24 (IANS): A so-called configuration change at the back-end forced some Facebook users to log out of their accounts unexpectedly, according to the social network.

The problem started on Friday and went on till Saturday for Facebook users, before it got resolved.

"On January 22, a configuration change caused some people to be logged out of their Facebook accounts. We investigated the issue and fixed it. We're sorry for the inconvenience," Facebook said in a statement on Saturday.

The affected Facebook users on Reddit reported they were receiving "sign in" prompts from their Facebook apps, but they had not signed out.

"We're looking into reports of people being logged out and having to login again to access their Facebook accounts. We're working to resolve this issue as quickly as possible. Thank you for your patience," Facebook tweeted.

According to Engadget, the iPhone users appeared most affected by the log-out issue,.

The users on iOS app were having difficulty logging back into their accounts when using two-factor authentication.

"Based on social media posts, many of the people with two-factor authentication enabled were eventually able to log back in, but the SMS codes were very slow to send, and some have had to upload pictures of their ID to regain access".

It was a "configuration change", admitted Facebook in a later tweet, thanking engineers "who fixed the issue and patiently tried to explain the cause to us to no avail".