Josh Miller/CNET

Apple and Samsung were fined Wednesday for software updates that Italy's antitrust watchdog said slowed down users' phones.

The Italian Competition Authority, or AGCM, fined Apple and Samsung 5 million euros (about $5.7 million) each for releasing software updates that "significantly reduced" the performance of phones, the AGCM said in a statement.

Both companies urged people to install updates that weren't "adequately supported by their devices," the AGCM said, adding that Apple and Samsung failed to provide customers with an "effective way to recover the full functionality of their devices." This pushed consumers to buy new devices, according to the AGCM.

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Apple was fined an additional 5 million euros for allegedly failing to provide adequate information on how to maintain and replace phone batteries.

Last December, Apple acknowledged that its iOS software slows down the performance of older iPhones. The company says iOS does this to counteract problems in aging lithium-ion batteries. After facing criticism over its battery policies, Apple apologized formally and offered battery replacements for $29, a program set to end Dec. 31.

Apple has denied that phones were slowed in order to get customers to buy new models. The company didn't respond to a request for comment.

Samsung denied it slowed down phones and said it will appeal the decision.

"We are disappointed with the Italian Competition Authority ... decision," a Samsung spokesperson said in an email statement. "Samsung did not issue any software update that reduced the Galaxy Note 4's performance. In contrast, Samsung has always released software updates enabling our customers to have the best experience possible."

Both smartphone makers were also ordered to publish a declaration on the Italian page of their websites informing consumers about the AGCM's decision.

First published Oct. 24, 10:03 a.m. PT.

Update, Oct. 24 at 10:47 a.m. PT: Adds Samsung's statement.

Update, Oct. 25 at 7:04 a.m. PT: Adds background about Apple's battery replacements and information from the AGCM.