Twitter will expand its advertising program for the Apple Inc iPhone and Google Inc Android devices, hoping to better tap into its growing mobile user base and ramp up revenue.

The company, which sells promoted tweets and advertises promoted accounts for customers, will now include both features on its mobile applications timeline, it said in a blogpost on Tuesday.

Until now, promoted trends and promoted tweets were included only on a search page when accessing Twitter on the iPhone or Android.

As a growing number of users switch to mobile phones and tablets as their primary method of accessing the Internet, ad-supported Web services are turning to mobile screens. About 55 percent of Twitter's over 100 million monthly active users access its service over a mobile phone.

Facebook, which gets almost 85 percent of its revenue from advertising on its website, is also reported to have been testing advertising for its mobile app.

San Francisco-based Twitter has already begun displaying promoted accounts for its iPhone and Twitter clients and will start publishing promoted tweets in coming weeks.

Initially, only a small number of users will see promoted tweets on their mobile phones, Twitter said on it blogpost.

Since 2010, Twitter's in-house sales staff has sold promoted tweets to large businesses on a case-by-case basis, but this month, the company launched a similar service to allow small businesses to buy and place ads on the online messaging platform.

The company's service lets people send 140-character messages, or tweets, to groups of followers. Twitter has more than 100 million active users and a valuation topping $8 billion, even though it does not yet have a significant money-making model.

(Reporting by Himank Sharma in Bangalore)