By Josh Ong

Published: 11:45 PM EST (08:45 PM PST)

The U.S. Department of Justice has concluded an antitrust investigation into Google's bid for a collection of wireless-related patents from Nortel and has approved the bid, while talks with Apple and Research in Motion over their potential bids remain ongoing.

Sources familiar with the DOJ investigation told The Wall Street Journal on Tuesday that Google has been given the go-ahead on its $900 million starting bid in an auction of over 6,000 patents from Canadian telecommunications-equipment maker Nortel.

Earlier this month, the Journal reported that the DOJ hadn't found any "major competitive" issues with Google and was actually more concerned about Apple. Sources said Apple and RIM have been in talks with the Justice Department, but gave no indication on how the talks were proceeding.

RIM is believed to be preparing to bid, as co-CEO Mike Lazaridis has called Nortel's LTE patents a "national treasure." Sources have also suggested that Apple is expected to bid on the patents. The DOJ is reportedly worried about Apple or RIM winning the auction because both companies have a reputation for being aggressive with the intellectual property.

The auction is set to take place on June 20, with Google's "stalking horse" bid to serve as the opening amount. The patent trove contains key components of the fourth-generation Long Term Evolution wireless technology.

“Google is a relatively young company, and although we have a growing number of patents, many of our competitors have larger portfolios given their longer histories,” Google general counsel Kent Walker said in April. “So after a lot of thought, we’ve decided to bid for Nortel’s patent portfolio in the company’s bankruptcy auction."

On Monday, Microsoft, AT&T and Verizon filed objections to the sale, claiming it would affect essential technologies and provide the winner with an unfair advantage over its competitors, the report noted. HP and Nokia have also filed objections.

Legal experts have compared the patents to an arsenal of nuclear weapons. The auction's winner "will have a very important stockpile of weaponry to countersue, said Alexander Poltorak, chief executive officer of General Patent Corp., which is not involved in the case. "That will keep a lot of potential aggressors at bay."

Tuesday saw the wrapping up of a high-profile legal dispute over patents between Nokia and Apple. After being at odds with Apple for years, Nokia announced that it had reached an agreement with Apple to put to rest all legal disagreements between each other. As part of the agreement, Apple will make a one-time payment and additional on-going royalties to Nokia.