E-commerce giant Rakuten said there are now more than 600 million registered users for its Viber messaging app, as growth has accelerated worldwide.

Revealing that its total stood at 608 million as of 31 July 2014, up from 400 million at the end of December 2013, Hiroshi Mikitani, CEO of Rakuten, noted that this is not necessarily its preferred metric.

“Some of the messaging apps companies are using a very similar number, so just to make it convenient, to compare apples with apples, we thought that maybe it was worthwhile to present the pure registration numbers,” he said.

Rakuten also provided a figure for “Unique IDs”, which stood at 400 million at the end of July – up from 280 million six months earlier.

“The growth is accelerating, especially in countries like India, Russia, the Latin American countries, in Southeast Asian countries,” the CEO said.

“Viber is reaching its monetisation target as well,” he continued.

Mikitani also said that work is underway to integrate Rakuten and Viber IDs, in order to extend its e-commerce and digital content businesses “using Viber as a funnel to reach out to the customer”.

“I think this is a very, very unique experiment, and this can completely change the growth pattern of the Rakuten business,” he said.

Rakuten inked its deal to acquire Viber for $900 million in February 2014, just days before Facebook announced its $19 billion megadeal to buy WhatsApp.

At the time the Japanese company said the deal was intended to strengthen its commerce platform by integrating it with the Viber user base.