Only a small number of the first generation iPods have the fault
Apple has admitted that a battery fault had led to a small number of its first generation iPod Nanos overheating.
But it said that the problem was "rare", occurring in 0.001% of devices sold between 2005 and 2006 adding there had been no serious injuries or damage.
The comments came after the Japanese government began investigating a possible battery defect in the Nano.
There have been two reports of the music players overheating in Tokyo, scorching nearby paper.
Economy, Trade and Industry ministry official Hiroyuki Yoshitsune said the government was in touch with Apple to investigate the defect.
Apple said the overheating problem, which could lead to the iPod failing to work and being damaged, could be traced to a single battery supplier.
"There have been no reports of serious injuries or property damage, and no reports of incidents for any other iPod Nano model," it said.
Any customer worried about their device, bought between September 2005 and December 2006, should contact customer services, Apple added.
Lithium-ion batteries, which are used in iPods, have been blamed for a series of fires in laptops, which resulted in global recalls.
In 2006, Apple was forced to recall some 1.8 million lithium-ion Sony-made laptop batteries that were prone to overheating.