Prime Minister Shinzo Abe has warned that North Korea may be capable of firing a missile loaded with sarin nerve gas toward Japan.
"There is a possibility that North Korea is already capable of shooting missiles with sarin as warheads," Mr Abe told a parliamentary panel on national security and diplomacy.
Mr Abe was responding to a question about Japan's readiness at a time of increased regional tension.
A US navy aircraft carrier is heading toward the Korean Peninsula as Pyongyang prepares for the 105th anniversary of the birth of its founder Kim Il Sung this weekend.
Citing Syria where dozens of people died recently in an alleged sarin nerve gas attack, Mr Abe said Japan should take the example seriously - stressing the need to strengthen its deterrence against the North.
North Korea, which is not a signatory to the international Chemical Weapons Convention, has been producing chemical weapons since the 1980s and is now estimated to have as many as 5,000 tons, according to a South Korean defence white paper.
Its stockpile reportedly has 25 types of agents, including sarin.
Experts say if North Korea were to attack South Korea, it would likely target Seoul's defences with chemical and biological weapons dropped from aircraft or delivered via missiles, artillery and grenades.
Japan, under its postwar constitution, has limited the role of its military to self-defence only and relied on the US for offensive and nuclear capability.
But recently, Mr Abe's ruling party has proposed that Japan should bolster its missile defence, including upgrading the capability to shoot down an enemy missile and acquiring the capacity to attack the base it was fired from.
With President Donald Trump's administration not ruling out a military option to dealing with North Korea, "tension is certainly rising", Mr Abe said to a group of politicians from his ruling party who sought increased safety measures for Japanese nationals in case of an emergency.