Apple Inc. will shut down the Quattro Wireless advertising network it acquired earlier this year and will support its new iAd network exclusively as of Sept. 30, according to a letter Apple sent to Quattro clients Thursday.

The move was widely expected because the Quattro Wireless team had been key in helping to develop iAd, a new service that Apple started on July 1. IAd delivers interactive rich-media ads inside iPhone and iPod touch apps.

“We believe iAd is the best mobile ad network in the world, and starting next month we’re going to focus all of our resources on the iAd advertising platform,” said Andy Miller, Quattro’s former chief executive who is now vice president of iAd for Apple, in the letter to Quattro clients.

The Business Insider news website earlier reported Apple’s plans to close Quattro.

IAd has been slow to take off, as Apple’s tight control over the creative aspect of ad making resulted in some delays, according to ad executives and other people familiar with the matter. But some of the first brands to come out with iAds, such as car maker Nissan Motor Co., have reported a high rate of users clicking on the ads.