Japan will consider increasing the pace of upgrades to its ballistic missile defense system in cooperation with the United States as the allies race to meet the threat posed by an effective increase in the speed of North Korean missiles, a Japanese government source said.

A proposal to adopt a land-based Aegis missile defense system known as Aegis Ashore will be the main topic of a Japan-U.S. foreign and defense ministers' meeting in Washington next month, the source said Sunday.

The Defense Ministry will request a budget for fiscal 2018 starting in April to include funds required to prepare for an Aegis Ashore deployment, according to the source.

The number of Maritime Self-Defense Force ships with the Aegis missile defense system may not be enough to shield all of the Japan against North Korean ballistic missiles if they are launched with a higher trajectory to make them fall faster and at a steeper angle, the source said.

Japan now has six Aegis destroyers, with four capable of intercepting ballistic missiles. The government is upgrading the remaining two destroyers to give them the same capabilities and plans to deploy two new ones.

While the Aegis system uses SM-3 missiles, Tokyo and Washington are jointly developing SM-3 Block 2A missiles with improved coverage and accuracy.

A North Korean missile launched on May 14, believed to be a new medium-range type, traveled some 800 km before falling into the Sea of Japan after reaching an altitude of over 2,000 km, according to the Defense Ministry.