Amazon is warning British customers that their hoverboards may be unsafe, the latest in a string of warnings about the popular scooters.

Amazon says some of the boards it sold are unsafe because they have "a non-compliant U.K. plug" and should be disposed of at a recycling center.

Amazon also says British officials have expressed concerns about the safety of hoverboards' rechargeable lithium batteries.

The skateboard-sized, motorized, two-wheeled scooters are increasingly popular, but concerns have been raised about their safety.

Britain's National Trading Standards agency said this month that 15,000 of the 17,000 scooters it had examined since Oct. 15 had been seized, mainly for having electrical components that could explode or catch fire.

British prosecutors also say it is illegal to ride hoverboards on both roads and sidewalks.