Messaging app WhatsApp was back in service late on Wednesday after a global outage knocked the 1.2 billion-member service offline across the world for several hours.

“Earlier today, WhatsApp users in all parts of the world were unable to access WhatsApp for a few hours. We have now fixed the issue and apologize for the inconvenience,” a WhatsApp spokesperson said in an email.

The spokesperson told Business Insider the outage was caused by WhatsApp itself, rather than by an “external source.” Asked if the outage affected all of WhatsApp’s users, the spokesperson reiterated that it was a “global” outage, but said it was not possible to say whether every user was affected.

The Facebook-owned messaging app is among the most popular communications tools in the world, with more than one billion users. The app stopped working around 4:50 p.m. ET on Wednesday.

Wednesday's outage occurred just as Facebook's senior management was on a quarterly-earnings conference call with Wall Street analysts and investors. Facebook touted the popularity of new WhatsApp features during the call, never mentioning the big outage underway that very moment.

WhatsApp users immediately took to Twitter to voice their frustrations:

https://twitter.com/stevieweviee/status/859882923830464515https://twitter.com/xsarah87x/status/859878025558720512https://twitter.com/SavanThammaiah/status/859876474769330181

https://twitter.com/Mily_Martinez_/status/859886769373949958