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

The move preceded a recall by Apple Computer Inc. (AAPL) Thursday of 1.8 million Sony-built laptop batteries that could overheat and catch fire.

Cupertino, Calif.-based Apple has received nine reports of the lithium-ion batteries battery packs overheating, including two consumers who received minor burns after handling overheated computers.

Apple has also received reports of minor property damage, but no serious injuries have been reported.

The Japanese 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.