Decision raises possibility Japan would create its own first-strike capability, which some say violates its constitution

Japan has scrapped plans to buy a multibillion-dollar missile defence system from the US that was intended to boost its ability to counter the “serious and imminent” threat posed by North Korea.

Japan’s defence minister, Taro Kono, conceded the land-based Aegis Ashore system would prove too costly and time consuming because it would require a hardware upgrade to ensure booster rockets did not fall on populated areas near host sites.

Related: North Korea's new warheads could penetrate missile shield, says Japan