OTT messaging service WhatsApp has passed the 250 million active user mark, the company told the Wall Street Journal.

This is the first time the company has revealed its user figures since it launched four years ago, although it revealed last week that it recently reached 27 billion messages processed in a single 24 hour period.

The user figure is more impressive given its lack of marketing spend and puts the messaging app above Twitter’s 200 million monthly active users announced at the end of last year. However, Microsoft said in October that its Skype video-chat service has 280 million monthly active users.

Despite the success of WhatsApp, it was reported earlier this week that Saudi Arabia’s national authorities have plans to block the service if it continues to fail to meet local regulations.

The growth of free messaging apps that use Wi-Fi or mobile data to send messages is a concern for operators as they are impacting revenue traditionally generated by SMS messages and voice calls. Indeed, a report from Chetan Sharma Consulting this week said that WhatsApp has “moved around” more messages than all mobile operators combined in any country – including the US and China – during the last 12 months.