By Poornima Gupta

(Reuters) - Singapore Telecommunications Ltd <STEL.SI>, Southeast Asia's largest telecoms company, has acquired a Silicon Valley startup in the mobile advertising sector, its second such purchase in two months.

SingTel's Amobee unit said on Tuesday it bought AdJitsu, which provides tools to make three-dimensional animated ads in mobile apps for iPhone and iPads. The acquisition of AdJitsu follows SingTel's purchase of mobile advertising firm Amobee in March for $321 million.

Terms of the latest deal were not disclosed.

AdJitsu will be folded into Redwood City, California-based Amobee, according to both companies.

AdJitsu was a unit of Palo Alto, California-based startup Cooliris, which has raised $28 million from big venture capital names such as Kleiner Perkins Caufield & Byers, DAG Ventures and The Westly Group.

Cooliris Chief Executive Soujanya Bhumkar said mobile advertising is seeing a lot of activity with advertising networks and media content providers jostling to gain a foothold.

"The space is hot right now," Bhumkar said. "The numbers are actually insane in terms of both economics and engagement."

In less than a year, AdJitsu has snagged major clients, including carmaker BMW and mobile handset maker Nokia.

Bhumkar said Cooliris sold AdJitsu -- a business-to-business unit -- to focus on its consumer-oriented divisions.

Cooliris started as a service to view photo and video content on the Web in a more visually appealing "3D Wall" but branched out to start AdJitsu and a photo-sharing app called Liveshare.

AdJitsu, which was spun off into a separate unit last December, has been receiving a lot of interest from both advertisers and ad networks, and growing at a rapid pace, Bhumkar said.

(Reporting By Poornima Gupta; editing by Edwin Chan, Jane Merriman and Steve Orlofsky)