TOKYO - A man was arrested on Saturday (Nov 6) for wielding an awl on a Tokyo subway train, just six days after a horrific Halloween attack on another train service left 17 injured and forced commuters to squeeze out of windows to flee.

Nobody was hurt in the latest incident on board a Tokyo Metro Tozai line train service.

But the man in his 50s had allegedly brandished the sharp object in a confrontation with two passengers, who he claimed had slighted him for not wearing a mask.

Tokyo has one of the world's lowest crime rates, but the Japanese capital has been hit by a wave of headline-grabbing violent attacks on its sprawling train network in recent months.

This has prompted deep soul-searching over the extent of security that is viable.

Chief Cabinet Secretary Hirokazu Matsuno condemned the Halloween attack as "brutal" and said his government will do all it can to prevent a repeat.

Yet, the authorities admit that there are manpower and cost limits in what can realistically be done.

Among the measures discussed at a September meeting between the Transport Ministry and train operators, held after a random knife attack in August left 10 injured, were to increase security patrols and install more surveillance cameras inside stations and carriages.

Artificial intelligence will also be tapped to detect suspicious people more effectively.

But all this is a work in progress.

The Mainichi daily, citing a source who attended the meeting, said that while it was ideal for security guards to keep a watchful eye at all stations, trains and carriages at all times, this was impractically difficult.

"Unless a passenger is obviously suspicious or in possession of dangerous goods, security officers cannot do random checks, especially at busy times like the rush-hour peak," a railway employee said.

The Yomiuri Shimbun said in an editorial last week: "It is difficult to completely prevent such crimes. But railway companies must apply their collective wisdom from the lessons learnt from successive incidents in implementing countermeasures."

In 1995, Japan suffered its worst domestic terrorism attack when the doomsday cult Aum Shinrikyo released sarin nerve gas during rush hour on three lines of the Tokyo Metro. The attack killed 14 and injured 5,500 others.

In 2015, a 71-year-old man self-immolated on a shinkansen bullet train bound for Shin-Osaka from Tokyo, leaving two dead and 28 injured.

Three years later, Ichiro Kojima, then 22, killed one and injured two others in a random knife rampage on board the shinkansen. The case led to new laws that ban bladed tools on trains if they are not properly wrapped up.

Yet, this did not prevent Yusuke Tsushima, 36, from going on an indiscriminate stabbing rampage on board an Odakyu Electric Railway train on Aug 6 this year.

Tsushima, who faces charges of attempted murder, had targeted "happy-looking women and couples" in the attack that left 10 passengers injured. He also tried to start a fire in the train using vegetable oil, but failed.

That same month, Hirotaka Hanamori, 25, who bore a years-long grudge against his junior, flung sulphuric acid at the latter's face at the Shirokane-Takanawa station. The junior suffered temporary blindness while a passer-by was also injured.

On Oct 15, a 45-year-old man stabbed two men at random outside the ticket gates at JR Ueno station.

And last Sunday, unemployed Kyota Hattori, 24, launched a Halloween attack on a Keio line train bound for Shinjuku, the world's busiest train station.

Hattori, who was dressed up as the villain character Joker from the Batman superhero series, said he was inspired by Tsushima's modus operandi in the knife and arson attack.

He told investigators that he wanted to kill "as many people as possible" in the hopes of getting the death penalty, and that he felt "vexed" at not succeeding in murder.

He first stabbed a 72-year-old man when he boarded the train, before setting a fire using lighter fluid.

Video footage on social media showed panicky commuters running away from a large blaze. They squeezed out of windows to flee after the train came to an emergency stop but with the doors kept closed.

The train operator said later that the doors were shut over safety concerns because they were not exactly aligned with the platform barrier doors, and there was a risk of passengers getting stuck in the platform gap.

The driver was also blinded by the absence of surveillance camera on that train.

The Asahi Shimbun said in an editorial last week that the attack was a "cautionary tale" that certain situations called for flexibility, while the Sankei Shimbun added that it was always crucial to secure an evacuation route for passengers.