Twitter is being investigated by US regulators over its dealings with third-party companies including UberMedia, the firm behind popular BlackBerry and iPhone apps.

The Federal Trade Commission is investigation whether Twitter's business relationships with other companies comply with US antitrust laws.

UberMedia, the firm behind popular Twitter apps UberSocial, Echofon and Twidroyd, has confirmed that it has been contacted by the FTC in relation to the probe.

"We have been contacted by the FTC and we intend to fully comply with their request for information," said a spokesman for UberMedia. "Beyond that, we have no further comment."

UberMedia, which has a fraught relationship with Twitter, is the first supplier to comment publicly on the FTC probe.

In February, Twitter banned a number of UberMedia's mobile apps with little notice.

Twitter made a number of changes including demanding that UberMedia change the name of its BlackBerry app, called UberTwitter, to UberSocial.

Weeks later, Twitter introduced strict new guidelines for all third-party developers using its data in a bid to retain more control over the platform.

Twitter also swooped to buy London-based Tweetdeck after reports emerged that UberMedia was close to sealing a deal.

Twitter sees its own official mobile apps and other "add-on" services, traditionally offered by third-party companies, as an important revenue stream while it tentatively introduces more advertising across the site.

Industry research firm eMarketer calculates that Twitter, which does not provide financial information, generated an estimated $45m (£28m) from advertising in 2010 and was expected to generate about $150m this year.

The importance placed by Twitter on third-party companies was underlined in May as it paid $40m to snap up TweetDeck

The FTC and Twitter have both declined to comment.