TOKYO -- The last six members of a Japanese doomsday cult who remained on death row were executed Thursday for a series of crimes in the 1990s including a sarin gas attack on Tokyo subways that killed 13 people and sickened more than 6,000 with symptoms that included being blinded or paralyzed.

Thirteen members of the group had received death sentences. The first seven, including cult leader Shoko Asahara, were hanged about three weeks ago. Japan has never executed so many people in one month, Justice Minister Yoko Kamikawa said. She called their crimes unprecedentedly heinous and said they should never be repeated.

The cult, which envisioned overthrowing the government, amassed an arsenal of chemical, biological and conventional weapons in anticipation of an apocalyptic showdown. Named Aum Shinrikyo, or Supreme Truth, it was blamed for 27 deaths before authorities raided its compound near Mount Fuji in 1995 and captured Asahara nearly two months later.

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The group's most notorious crime was the March 20, 1995, subway attack that sickened 6,000 people and sowed panic during the morning commute. The attack woke up a relatively safe country to the risk of urban terrorism.

Shoko Asahara, leader of Aum Shinri Kyo, appearing on NHK news program in March 1995, denying any involvement in the nerve gas attack on Tokyo's subways NHK/AP

Cult members used umbrellas to puncture plastic bags, releasing sarin, a deadly nerve agent developed by the Nazis, inside subway cars just as the trains approached the Kasumigaseki station, Japan's main government district. Commuters poured out of stations, and the streets were soon filled with troops in Hazmat suits and people being treated outside.

The toxin struck victims down in a matter of seconds, leaving them choking and vomitting, BBC News reports. In the following months, members of the cult carried out several failed attempts at releasing hydrogen cyanide in various stations.

Kamikawa said it was a terrorist attack that terrified people even outside Japan.

Four of the six executed Thursday released sarin on the subway. The two others were convicted in other crimes, including the 1989 murders of an anti-Aum lawyer and his wife and 1-year-old baby and a 1994 sarin attack in the city of Matsumoto in central Japan, which killed seven people and injured more than 140. An eighth victim in Matsumoto died after being in a coma for a decade.

The executions were announced only after they had happened, as is the practice in Japan.

Asahara, whose original name was Chizuo Matsumoto, founded Aum Shinrikyo in 1984. The bearded, self-proclaimed guru recruited scientists and others to his cult, attracting people who were disillusioned with a modern, materialistic lifestyle.

During an eight-year trial, he talked incoherently, occasionally babbling in broken English, and never acknowledged his responsibility or offered meaningful explanations.

The cult once claimed 10,000 members in Japan and 30,000 in Russia. It has disbanded, though nearly 2,000 people follow its rituals in three splinter groups, monitored by authorities.