A special committee under the Transport Ministry ordered the Teito Rapid Transit Authority to inspect all subway cars of the same type as the one that was involved in the fatal accident near Tokyo's Nakameguro Station on Wednesday morning.

The committee of experts did not specify the cause of the derailment in the day's meeting.

"I get the impression that it's quite difficult to specify the cause at this stage," said Masatomi Yasutomi, chief of the ministry's railway bureau, who attended the committee session. "I think the committee members are of the same impression."

It did, however, point out that air had been released from the rubber suspension system of the derailed carriage.

Later in the day Teito officials said they had confirmed that the air springs had not been punctured, that someone must have manually withdrawn air from the springs a few hours after the accident to ensure safety in jacking up the car.

Company investigators had confirmed that the suspension units had air in them during visual checks of the derailed train immediately after the accident, the officials said.

The springs had been visually checked on Sunday. They were due to be exchanged by 2001.

Teito officials also maintained that even if a sudden blow out of the springs had occurred, it only would have resulted in the cars tipping three cm to one side.

The ministry committee also ordered the subway operator to set up a barrier to prevent wheels from derailing at and around the spot where the accident occurred.

Teito officials have maintained that the curve where the collision occurred is not extreme and that the law does not require derailment prevention rails at the site.

But they said they would lay the additional rails overnight and conduct suspension maintenance checks around the clock so that trains will be ready to run from Nakameguro to Ebisu stations today.

"We have to be sure trains run in the morning," said Hirosada Haku, chief of the engineering administration section of Teito.

The authority oversees operations on the Hibiya Line, which 1.1 million people ride daily. Over 300,000 commuters use Nakameguro Station every day, Teito officials said.

The officials said that its train, bound for Yokohama's Kikuna Station, was traveling between 25 kph and 40 kph when it derailed.

"We cannot understand why a derailment would occur at that speed," Nojiri said.

A safety system is installed to slow trains down as they approach the station, the officials said, making it impossible for the train to have been traveling more than 40 kph at the time of derailment.

Commenting on the cause of the collision, the officials said that train tracks are laid out to maintain a 72 cm space between passing trains.

"This is within legal safety standards set by the Transport Ministry," Nojiri said.

The committee said trains should run at a slower speed of 15 kph at the spot to confirm the tracks' safety until all examinations are finished.

The train derailed from the track as it ran on a curve equivalent to that of a circle with a radius of about 160 meters, which is relatively sharp for a railroad, according to ministry officials.

The committee also recommended that the subway operator check a lubricating oil supplier at the curve, which is supposed to automatically provide oil when a train approaches, the officials said.