TOKYO (AP) _ Helicopters patrolled Tokyo's skies and police stood watch over major intersections Saturday because of fears that the cult suspected in a nerve gas attack on Tokyo's subways might strike again.

Streets and subway trains were unusually empty, and shopping centers and several schools in Tokyo's central Shinjuku district were closed due to the threat of a possible attack. As a precaution, hospitals reportedly were ordered to stock up on nerve gas antidotes.

In a highly unusual move, Prime Minister Tomiichi Murayama directed officials to tighten security in the capital, according to the Kyodo News Service.

Chief government spokesman Kozo Igarashi said the fears may be baseless. ``But we must be cautious about everything so that the people can be free of worry,'' he said Friday.

The cult, called Aum Shinri Kyo, or Supreme Truth, has repeatedly denied involvement in subway terror and denounced violence.

But evidence linking it to the kind of nerve gas used in the March 20 attack, which killed 11 people and sickened thousands, has made the cult the target of Japan's most intense criminal investigation ever.

It also has focused the nation's attention on a prophecy by cult leader Shoko Asahara that disaster will strike Tokyo on Saturday. Made in a book published last month, the prophecy spoke of an earthquake. But several reports this week have said Asahara also has predicted a ``horrible'' event in Shinjuku, one of Tokyo's most popular entertainment districts.

The prophecy heightened anxieties in a city still stunned by the subway attack and the near-fatal shooting of Japan's top police official 10 days later.

Some shopping centers and schools in Shinjuku closed early Friday.

``My friends said I shouldn't come into work today,'' said Nobuko Ogawa, a department store employee on the job Saturday. ``It's a bit scary, but I think everything will be OK.''

Most stores hired private, uniformed security guards who patrolled the near-empty shopping aisles.

``Luckily my family lives in the countryside and hasn't heard anything about all this,'' Ogawa said, speaking next to a counter. No customers were in sight.

The government instructed hospitals to stockpile nerve gas antidotes and train personnel in preparation for a possible attack, according to a report Friday in the Yomiuri, Japan's largest circulation newspaper.

Police patrols have been beefed up in Tokyo, tens of thousands of police manned roadblocks nationwide, and thousands more conducted raids Friday at more than 130 facilities.

In one of those raids, at the cult's main commune at the foot of Mount Fuji, police carried away 53 children _ many wearing headgear with wires attached, which cult followers believe allows them to synchronize brain waves with Asahara's.

Eight of the children were hospitalized for malnourishment, including several who had pneumonia, reports said.

Almost daily searches at several cult facilities since the attack have turned up tons of chemicals and equipment police say could have been used to make nerve gas.

Police also claim to have found chemicals and documents that could indicate the cult was experimenting with biological weapons and was trying to manufacture its own guns.

The cult says at least 107 of its members have been arrested on a variety of charges, none directly related to the subway attack or the shooting, and claim the police actions are religious oppression.

Early Saturday, police announced the arrest of cult member Masanobu Iwao, 35, on suspicion of breaking into a laser research center, the Kyodo News Service said.

Though Asahara's whereabouts remain unknown, so far at least three of his top disciples and one senior member who was formerly a member of Japan's largest gangster syndicate have been taken into custody.

Most of those arrests were also for unrelated, minor crimes _ one for riding a stolen bicycle, another for using a false name in a hotel register.

``Police are supposed to gather evidence, and make arrests based on that evidence,'' said Fumihiro Joyu, the cult's spokesman. ``But this time, they're just attacking us, and making up reasons to dismantle our property.''

Asahara predicts a war between Christians and Buddhists will set off World War III in 1997, and says sect followers must prepare to survive.