Google on Thursday announced it has bought advertising technology startup Invite Media, which allows advertisers to bid on ad space.

Invite Media developed a way to let advertisers bid in real time for online display ad space and created a "universal buying platform."

"We're investing significantly in the display advertising ecosystem and are seeing great momentum," Google vice president of product management Neal Mohan said in a blog post.

"Real-time bidding technology is an important part of this ecosystem."

Google plans to invest heavily in Invite and eventually mesh its technology into DoubleClick, an online ad-targeting business it acquired three years ago.

Financial details of the Invite deal were not disclosed but reports put the price tag at 70 million dollars (US). Invite was founded in Philadelphia and has offices in New York City.

Internet rights group Center for Digital Democracy has called on the US Federal Trade Commission to investigate Google's purchase of Invite Media, saying the deal raises competitive and privacy concerns.

"The ink is hardly dry on Google’s questionable AdMob acquisition and the Internet giant is forging ahead with an insatiable appetite for more," said John Simpson, a consumer advocate for the nonprofit group.

Last week, Google said it had completed its 750-million-dollar purchase of mobile advertising network AdMob and is eagerly integrating its technology into its services.

Google hopes AdMob will help it more effectively extend its lucrative Internet advertising domain into the booming world of mobile devices.

"The FTC blinked in the face of Google's Washington clout on the AdMob deal," Simpson said. "It's time for the commissioners to stand firm and give Google the scrutiny it deserves."