A Japanese government ministry Thursday ordered Sony Corp. and Dell Inc. to look into what went wrong in the Sony batteries that've caused some Dell portable PCs to burst into flames in Japan and elsewhere, adding to the two companies' woes.

The Ministry of Economy, Trade, and Industry (METI) told the pair that they had to report back their findings and outline how they will prevent future problems with on-fire laptops by the end of this month or face fines, several news services reported.

In a statement released Thursday, METI said that in two incidents -- one in Oct. 2005, the other in June of this year -- Sony batteries in Dell notebooks overheated and caught fire. No injuries were reported in either case. The government agency told Dell to investigate the safety of its Inspiron, Latitude, and Precision portable lines.

Last week, Dell issued a recall of 4.1 million Sony-made batteries for notebooks sold between April 2004 and July 2006. It was the largest computer-related recall ever ordered by the U.S. Consumer Product Safety Commission.

In early trading, Dell's shares fell by 0.6 percent, or 12 cents, to $21.52. Sony, meanwhile, dropped 2.8 percent, or $1.24, to $43.18.