The Japanese government plans to acquire up to 400 US-made Tomahawk cruise missiles to help boost counterstrike capabilities.
Members of the ruling coalition disclosed this during a directors' meeting of the Lower House budget committee on Monday.
They said 400 is the maximum number and the actual figure will be decided later.
The disclosure came after the main opposition Constitutional Democratic Party urged the government last week to announce how many missiles it plans to buy.
Prime Minister Kishida Fumio replied that the matter attracts much public interest, and the government will decide whether to make an announcement.
The opposition party also requested that the government present concrete examples of cases in which the country would exercise its counterattack capabilities.
But the government declined, saying that disclosing such details could undermine national security.