Japanese Prime Minister Shinzo Abe has said North Korea may be capable of arming missiles with the chemical weapon sarin, the same nerve agent used against Syrian civilians last week, Reuters reports.

Speaking to a session of parliament, Abe said “There is a possibility that North Korea already has a capability to deliver missiles with sarin as warheads.” His comments come at a time of increasing concern over a potential sixth North Korean nuclear weapons test, and heightening military tensions between South Korea, Japan, the United States, and North Korea.

Japan was itself the victim of a sarin gas attack in 1995, when a domestic terrorist cult organization called Aum Shinrikyo released sarin into the Tokyo subway system, killing 12 people and making thousands sick. The same group had used sarin the year prior in another attack, killing 8.

Abe provided no specific evidence that the North Koreans possessed the capability or intended to launch a chemical weapons attack on Japan, but North Korea is widely known to possess stocks of chemical weapons. It never signed the Chemical Weapons Convention, and experts believe they possess up to 5,000 tons of chemical weapons.