Apple's Japanese unit has promised to improve website warnings over its first-generation iPod Nano music player after incidents of it overheating and catching fire, a government statement said.

The Ministry of Economy, Trade and Industry said in a weekend press release that Apple Japan had submitted a report about measures it has taken against the incidents - such as giving warnings or recalling the products.

The report was filed in response to an order issued a week ago by the ministry after recharging problems caused 27 overheating incidents, including six fires, which left four people with minor burns.

"The ministry is in the process of closely examining the report and making additional inquiries to the company," the statement said.

Apple has sold about 1.8 million units of the 2005 iPoD Nano model in Japan since September 2005.

The Japanese unit has put information on its website about the problems, including recommending battery replacements. However, the lack of prominence given to the warnings has provoked criticism.

The ministry statement said that Apple Japan has vowed to "improve the homepage in a way to make it easy for users to understand with regard to warnings and measures to prevent recurrences of incidents."

It also noted that the company had newly notified the ministry of 34 other "non-serious" overheating accidents. The ministry called the delay "truly regrettable."

The latest setback for Apple follows the launch of its iPhone 4, which has been dogged by reception problems linked to its new design and manufacturing issues that have led to the delay of the white version.