Google's acquisition of Admeld, a company that provides an advertising platform for publishers, is coming under increased antitrust scrutiny from the US Department of Justice.

Google said in a blog post late Wednesday that the department has asked the Internet search and advertising giant for more information about the deal.

Google announced the acquisition of Admeld last month. The purchase price was not revealed but technology blog TechCrunch put it at around $400 million.

"We've been discussing this deal with the Department of Justice, who are obliged to review the transaction because of its purchase price," Neal Mohan, Google's vice president of display advertising, said in the blog post.

"As they do for many acquisitions, they have sent us a 'second request,' which means that they are asking for more information in order to complete their review of this particular acquisition," Mohan said.

"This doesn't surprise us, as today's display advertising industry is very new and highly complex," he said. "But we'll work to enable this review to be concluded as quickly as possible."

Admeld chief executive Michael Barrett said he was confident the deal would be cleared but was "disappointed by this decision because it will delay our efforts to bring even more innovative services to our clients and partners."

The Mountain View, California-based Google makes most of its money from advertising tied to Internet search but is seeking to carve out a bigger slice of the market for display advertising, which includes rich media, digital video and banner ads.

Mohan said Google believes the display advertising business "is, and will remain, extremely competitive."

"In fact, since we announced this acquisition about a month ago, at least three new and expanded platforms for buyers and publishers have been launched," he said. "Others continue to grow."

According to digital marketing firm eMarketer, Facebook is on track to pass Yahoo! in US display advertising revenue this year while Google will also gain market share.

Facebook's share of US online display ad revenue will grow to 17.7 percent this year, up from 12.2 percent last year, while Yahoo!'s share is expected to decline to 13.1 percent in 2011 from 14.4 percent last year, eMarketer said.

Google's share of US display advertising revenue will grow to 9.3 percent this year from 8.6 percent last year, eMarketer said.

Google has come in for increasing regulatory review in the United States and Europe as it has grown from a scrappy startup into an Internet titan.

Among the deals that have drawn scrutiny are Google's $3.1 billion purchase of online ad firm DoubleClick, its $750 million buy of mobile ad network AdMob and its $700 million acquisition of flight data company ITA Software.

In 2008, Google was forced to drop plans for a joint search advertising partnership with Yahoo! amid opposition from the Justice Department.

Google also announced last month that it was cooperating with a US Federal Trade Commission probe into its search and advertising business.