The Japanese government says Pyongyang appears to be developing warheads capable of penetrating its defensive ballistic missile shield.

Japanese defense chief, Takeshi Iwaya made the claim on Tuesday, citing the irregular trajectories of the latest missiles launched by North Korea. Iwaya told a news conference that Japan believes the rockets were a new short-range ballistic missile.

Recent short-range missile tests by Pyongyang have stoked alarm in neighbouring Japan even as United States President, Donald Trump has dismissed the launches as unimportant.

Saturday’s test firings came a day after Seoul said it was ending a military intelligence-sharing pact with Tokyo amid a worsening spat over wartime forced labour.

Japan and the US have deployed Aegis destroyers in the Sea of Japan armed with interceptor missiles designed to destroy warheads in space. Japan also plans to build two land-based Aegis batteries to bolster its ballistic missile shield.

These defense systems are however designed to counter projectiles on regular and therefore predictable trajectories and any variation in flight path would make interception trickier.

On Tuesday, an official of South Korea’s defense ministry said the US is currently running a detailed analysis of the latest North Korean launches.