Facebook said the problem that stopped it, Instagram and WhatsApp from working has now been fixed.

But it is yet to explain the problem in detail, saying only that it had "triggered an issue".

The outage meant that users of all three platforms were unable to send or see images, videos and other files. It hit all of the different platforms in different ways, and while the sites loaded specific parts of them did not work.

As the outage was going on, it posted a vague explanation of the problem.

"During one of our routine maintenance operations, we triggered an issue that is making it difficult for some people to upload or send photos and videos," Facebook had said.

Later, after the problem was fixed, it gave another update on the issue on Twitter. It explained even less about the issue and said only that it apologised for any problems.

"Earlier today, some people and businesses experienced trouble uploading or sending images, videos and other files on our apps and platforms," it posted. "The issue has since been resolved and we should be back at 100% for everyone. We're sorry for any inconvenience."

"The disruption appears to be related to an internal infrastructure or application issue," said ThousandEyes, a company that monitors internet traffic globally.

Facebook, which gets tens of millions of dollars from advertising revenue daily, declined to comment when asked whether it will refund businesses. In a similar incident in March, the company said it would consider refunding advertisers for lost exposure.

Back then, Facebook was also vague in its explanation of the problem. "Yesterday, as a result of a server configuration change, many people had trouble accessing our apps and services," it said after it was fixed, before apologising for any problems.

This time around, the partial outage frustrated users of the world's largest social network, with many taking to Twitter to complain.

More than 14,000 users reported issues with Instagram, while more than 7,500 and 1,600 users complained about Facebook and WhatsApp, according to outage tracking website Downdetector.com.

Downdetector's live outage map showed the issues were mainly in parts of Europe and the United States.

Additional reporting by agencies