Amazon.com, in an apparent switch in its pricing policy, said over the weekend that it will allow purchasers of its new Kindle Fire tablets to pay $15 extra to turn off advertisements that are built into the devices.

The change came barely a day after Amazon on Thursday unveiled larger Kindle Fire tablets, priced from $159 to $599, to challenge Apple Inc's dominant iPad on price and additional digital content.

Amazon had said the tablets would come with ads known as "special offers" that appear when screens are locked and in the corner of the home screen, helping keep prices low. But criticism of the company mounted in online forums after reports that the company would not allow buyers to pay to block the ads as it had done with earlier tablets.

By Saturday web sites engadget.com and cnet.com were reporting that Amazon had changed its policy.

In an email response to questions from Reuters, Amazon spokesman Kinley Pearsall said only: "With Kindle Fire and Kindle Fire HD there will be a special offers opt-out option for $15. We know from our Kindle reader line that customers love our special offers and very few people choose to opt out. We're happy to offer customers the choice."

Amazon unveiled the new wireless tablets without having received approval for their sale from the Federal Communications Commission, which requires that products operate safely and won't interfere with other signals. The company said it expects to receive the approval in time to meet its planned shipping date of November 20.