Japan's trade ministry on Thursday ordered Sony Corp. and Dell Inc. to investigate the trouble involving Sony batteries that caused Dell to recall 4.1 million laptop power packs last week because they were at risk of catching fire.

The batteries in question, made by Sony Corp., are in notebooks shipped between April 1, 2004, and July 18 of this year. The company said in a statement that the recall would affect approximately 95,000 battery packs sold to customers in Canada.

"In rare cases, a short-circuit could cause the battery to overheat, causing a risk of smoke and [or] fire," said Ira Williams, a Dell spokesman. "It happens in rare cases, but we opted to take this broad action immediately."

The ministry said Sony and Dell must report on their findings and say how they will prevent future problems by the end of August, or face a fine under Japan's consumer safety laws.

Lithium-ion batteries manufactured by Sony for Dell laptops imported to Japan overheated and caught fire in at least two separate instances in October and June, the Ministry of Economy, Trade and Industry said in a statement. No one was injured in those incidents, but the fires destroyed the machines, according to ministry official Atsuo Hirai.

The ministry also pointed to problems with battery cells supplied by Sony for Dell computers in other countries, and told the companies to investigate the safety of Dell models Latitude, Inspiron and Precision imported to Japan from April 2005.

The ministry also instructed other Japanese electronic makers to check the safety of their laptop batteries.

Battery packs contain cells of rolled up metal strips. Sony has said that during production, crimping the rolls left tiny shards of metal loose in the cells, and some of those shards can cause batteries to short-circuit.

Dell has already recalled batteries from affected models in Japan. Batteries powering Sony's Vaio laptops don't have the same problems, according to the Tokyo-based manufacturer.

The battery problems, which resulted in the largest recall of electronics-related products in U.S. history, have come as embarrassing news for Round Rock, Texas-based Dell, the world's largest PC maker, and for Sony, which has been trying to overhaul its electronics operations amid a slump in profits.

The recalled batteries were sold with the following Dell notebook computers: Dell Latitude D410, D500, D505, D510, D520, D600, D610, D620, D800, D810; Inspiron 6000, 8500, 8600, 9100, 9200, 9300, 500m, 510m, 600m, 6400, E1505, 700m, 710m, 9400, E1705; and Dell Precision M20, M60, M70 and M90 mobile workstations; and XPS, XPS Gen2, XPS M170 and XPS M1710.

Customers are advised to contact Dell immediately to determine if their notebook computer battery is part of this recall, at 1-866-342-0011 or on the web.

Customers may continue to use the notebook computers safely by turning the system off, ejecting the battery, and using the AC adapter and power cord to power the system until the replacement battery is received.