Mark Zuckerberg believes WhatsApp can reach two to three billion users once it becomes part of Facebook, reports The Wall Street Journal.

Speaking at an event in Mexico organised by Carlos Slim’s Telmex Foundation, the Facebook CEO said that WhatsApp would remain an independent service, but is likely to benefit from access to Facebook’s resources and its audience of 1.3 billion monthly active users.

The most recent figure for WhatsApp’s user base was given in April, when the number of monthly active users passed the 500 million mark.

Zuckerberg added that Facebook is prepared to spend “billions of dollars over the next decade” as part of its efforts to connect everyone in the world, something that will undoubtedly involve WhatsApp.

The $19 billion acquisition, which was agreed in February, is currently undergoing a review by the European Commission, which reportedly sent a second round of questionnaires to rival companies last week asking whether the deal could lead to price rises or restrict innovation.

The EC last week said it would deliver its decision about the merger by 3 October, after being officially notified of the transaction on 29 August.

EU competition commissioner Joaquin Almunia was quoted by Bloomberg today as saying the final decision “will not take a long time”, adding that it’s “not the most difficult merger” the regulator has had to deal with.

It was Facebook itself that asked the EC in May to conduct a review covering all 28 countries within the EU to avoid the possibility of separate reviews in multiple markets.

The social network giant said at the end of July that it may extend the deadline for closing the WhatsApp deal to 19 August 2015 if the applicable closing conditions, other than certain regulatory approvals, have been satisfied.

The US Federal Trade Commission (FTC) cleared the deal in April, but notified Facebook and WhatsApp about their obligations to protect consumer privacy, including the fact that post-merger WhatsApp must continue to honour prior promises made to consumers.