Amobee, a digital advertising firm fully owned by SingTel, said in a statement it had signed agreements to buy Adconion, a cross-channel digital advertising company as well as Kontera Technologies, a digital content intelligence and marketing technology firm.

Adconion Direct North America and Adconion Australia will be acquired for $235 million including debt, while US-based Kontera will cost $150 million.

Amobee said the deals are subject to certain conditions being met.

Allen Lew, chief executive of Group Digital Life at SingTel, said the purchases would enhance Amobee's ability to create digital marketing campaigns that can reach SingTel's global network of more than 500 million subscribers.

Adconion has top brands including Toyota, Disney and AT&T among its clients, while Kontera, which has a research and development centre in Israel, analyses consumer behaviour on social media.

SingTel bought Amobee in 2012 for $321 million and the firm holds a market share of about 10 percent of global ad spend in the mobile display advertisements sector, it said.

Lew, who is also Amobee's chairman, said SingTel has so far spent about a quarter of the Sg$2.0 billion allocated by its board for digital investments until the 2016 financial year.

SingTel's revenue from mobile advertising in the year to March 2013 stood at Sg$113 million ($90 million). Its net profit came in at Sg$3.65 billion, a 4.1 percent increase from the previous year.

The telco owns partial stakes in India's Bharti Airtel, Indonesia's Telkomsel, Thailand's Advanced Info Service, the Philippines' Globe Telecom and Pacific Bangladesh Telecom. It fully owns SingTel Optus in Australia.