Japan on Tuesday warned consumers over Apple’s iPod Nano portable music player after one of its ministries received three reports of minor fires caused by overheating devices.

The Ministry of Economy, Trade and Industry said it had begun an investigation into the incidents, which involved Nanos sold in the first year after the player’s launch in 2005. “There have been multiple cases of overheating and fire damage, in particular during recharging, so please use caution,” it said on its website.