U.S. antitrust regulators plan to investigate whether Apple is unfairly restricting rivals such as Google from carrying ads on the iPhone, iPad and iPod, the Financial Times said.

The regulators have already started scanning Apple's actions, the paper said, citing people familiar with the move.

But it is not yet clear whether the Federal Trade Commission or the Department of Justice would take up an investigation, the Times said.

Apple could not immediately be reached for comment by Reuters outside regular U.S. business hours.

On Wednesday, Google said recent changes to Apple's developers agreement would effectively cripple Google's advertising tools for the iPhone, creating artificial barriers to competition.

Apple changed the language of the agreement on Monday, which now appears to prohibit certain third-party ad agencies from collecting critical usage data from iPhone applications.

(Reporting by Sakthi Prasad in Bangalore; Editing by Mike Nesbit)