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Ruling party sources say Japan is leaning towards choosing the Aegis Ashore missile-defence system over another advanced system called Terminal High Altitude Area Defence (THAAD). The US THAAD system was made operational in South Korea last week in response to a growing missile threat from North Korea. But Japan appears to be considering the land-based version of the Aegis system developed for warships.

The Japanese government now favours the Aegis Ashore system as it comes with a wider coverage area, which would mean fewer units needed to protect Japan Sources

American aerospace company Lockheed Martin Corp makes both systems. Three government and two ruling party sources told Reuters the Japanese government now favours the Aegis Ashore system as it comes with a wider coverage area, which would mean fewer units needed to protect Japan. The sources, who spoke this week, declined to be identified because they are not authorised to speak to media on the topic.

AFP GETTY Japan is considering a new missile defence system to counter the North Korean threat

An Aegis Ashore unit costs about £480billion, while a THAAD unit costs more than £680billion yen, the sources said. The sources added the Aegis Ashore system would help reduce the burden of round-the-clock vigilance shouldered by Japanese warships. What is THAAD? Why is the US installing the THAAD missile system in South Korea?

GETTY The US THAAD system was made operational in South Korea last week

REUTERS Experts predict Kim Jong-un will carry out a sixth nuclear test this month

The government will make a final decision on the new defence system in coming months, after sending, possibly this month, an inspection team to Hawaii, where US forces operate Aegis Ashore test facilities. Japan's ruling Liberal Democratic Party in March urged Prime Minister Shinzo Abe's government to consider acquiring the capability to hit enemy bases and to beef up missile defence. The search for a new missile defence system comes as tensions continue to escalate between North Korea and the US over Pyongyang's nuclear and missile tests.

Kim Jong-un flexes his military muscles Mon, May 15, 2017 North Korean leader Kim Jong-un inspecting military detachments on two islets in waters off the country's southwest front. Play slideshow REUTERS 1 of 16 North Korean leader Kim Jong Un inspects the long-range strategic ballistic rocket Hwasong-12 (Mars-12)