Research In Motion confirmed on Friday that Japanese mobile operator NTT DoCoMo has halted sales of the BlackBerry Bold due to overheating. However it said that the battery wasn't the source of the problem.

Multiple press reports earlier on Friday reported that the overheating of the BlackBerry Bold was related to battery problems. However, RIM said in a statement that while "analysis of the devices in question has allowed [RIM and DoCoMo] to rule out a battery problem, the root cause remains under investigation."

The companies are investigating reports of some BlackBerry Bold devices sold in Japan "reaching warmer-than-usual device temperatures during charging." This issue appears to be specifically limited to BlackBerry Bold devices sold in Japan, and sales of Bold devices in other countries are unaffected by this matter.

DoCoMo has sold around 4,000 Bold units, with roughly 30 users issuing complaints regarding overheating during charging, wrote Avi Cohen, managing partner of financial analyst firm Avian Securities, in a research note.

However, this is not the first time problems have been reported with RIM's Bold device. UK mobile carrier Orange last year suspended shipment of BlackBerry Bold handsets after concerns were raised over 3G software problems.

DoCoMo started selling BlackBerry Bold devices in Japan last week and both companies hope to renew sales in Japan soon, RIM said. The phone is designed to provide access to DoCoMo's 3G network and also includes Wi-Fi and GPS (global positioning system) navigation capabilities. It also includes a keyboard and supports Japanese text input capabilities.

The BlackBerry Bold does not have inherent overheating problems, said Jack Gold, principal analyst at J. Gold Associates.

"To me that doesn't sound correct," said Gold, who also owns and uses a BlackBerry Bold.

He suspects the problem could be related to software or customisation of the phone for the local market, where the device has seen problems in the past. But it's fairly common for new products to have problems, Gold said. Motorola has slipped in launching products and Apple had to fix issues the original iPhone saw, he said.

Whatever the problem may be, RIM has to fix it quickly, Gold said. If its relaunch is delayed for a substantial number of months, it could lose significant market share, he said.