SAN FRANCISCO — Apple is further tightening its control of the App Store.

Some application developers, including Sony, say Apple has told them they can no longer sell e-books within their apps unless the transactions go through Apple’s system. Apple rejected Sony’s iPhone application, which would have let people buy and read e-books from the Sony Reader Store.

Apple said on Tuesday that it was still allowing customers to read e-books they bought elsewhere within apps. For example, a Sony app could still access books the customer bought earlier from Sony’s store.

But Steve Haber, president of Sony’s digital reading division, said on Monday that Apple had told his company that from now on, all in-app purchases would have to go through Apple.

“It’s the opposite of what we wanted to bring to the market,” Mr. Haber said. “We always wanted to bring the content to as many devices as possible, not one device to one store.”