Apple Inc is set to announce it has acquired mobile advertising company Quattro Wireless for $275 million, the Wall Street Journal-affiliated blog All Things Digital reported.

An announcement could come as early as Tuesday, said the report, which cited unnamed sources.

Apple did not respond to a request from Reuters for comment.

Quattro is a competitor to AdMob, which Google Inc agreed to acquire in November for $750 million. All Things Digital and other media outlets have reported Apple had also been trying to buy AdMob.

According to its Web site, Quattro's advertising network includes thousands of mobile Web sites, along with applications on Apple's iPhone and Google's Android platform, and other smartphones.

The company was started in 2006. Investors in Waltham, Massachusetts-based Quattro include venture capital firms Highland Capital Partners and Globespan Capital Partners.

Apple sits on more than $30 billion in cash and securities, but rarely makes acquisitions.

It bought digital music service Lala in December for an undisclosed amount. It acquired PA Semi, a designer of low-power microchips, in 2008 for a reported $278 million.