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The hoverboard controversy continues to heat up.

Amazon's UK division has asked some customers to throw out their hoverboards, the self-balancing scooters that have clambered onto holiday wish lists this season, due to safety problems with the devices.

"Please dispose of this product in a [recycling center] as soon as possible," read a company email sent to customers, which Amazon UK shared with CNET on Wednesday.

The notices come a few days after Amazon removed a handful of hoverboards from its US website, reportedly to ensure quality control of the devices. Amazon's US operations haven't confirmed the move, but hoverboard maker Swagway shared with news outlets information it said came from Amazon that describes the change.

On Wednesday, Amazon said the UK hoverboards were deemed unsafe due to a noncompliant plug for electrical outlets.

The warning serves as another knock against hoverboards, which have now raised safety concerns after reports that some have caught fire. The reported fires have been linked to overheating of the boards' lithium ion batteries.

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In the email to UK customers, Amazon said it has requested refunds on behalf of customers. If a customer purchased a hoverboard as a gift for someone, Amazon asked the customer to notify the recipient.

Amazon UK sent out a second email to other local customers who purchased hoverboards that have not had a safety problem, looking to provide some additional safety tips on using the product.

The Amazon UK emails were part of a growing list of actions taken by companies and regulators in response to hoverboard issues this holiday-shopping season. Online retailer Overstock.com said last week that it will no longer sell them because of safety concerns. Worries about battery fires have led to a ban of hoverboards by most major US airlines. American, Delta, Southwest and United said last week that the devices are not allowed in carry-on or checked baggage.

Also, the US Consumer Product Safety Commission has begun investigating whether faulty batteries are responsible for the fires. The UK Trading Standards agency has also raised concerns about the safety of some hoverboards.