Japan's defence minister on Friday visited US military bases on Guam.
Minister Tomomi Inada has been reported to be considering the purchase of a missile defense battery similar to the Terminal High-Altitude Area Defense system the Pentagon deployed to Guam more than two years ago.
The Marianas Variety reported that the US deployed the system in response to missile-launch threats from North Korea.
North Korea has threatened to launch missile attacks toward Guam and other US military bases in the Asia-Pacific region, including Japan and South Korea.
Japan's minister was also understood to have been updated on the progress of Japan government-funded projects in Guam for the relocation there of almost 5,000 US Marines from Okinawa.
Japan is paying US$2.8 billion of the estimated $8.6 billion cost to reduce the presence of U.S. Marines in Okinawa and move about 5,000 of the troops and their 1,300 dependants to Guam, according to the U.S.-Japan revised agreement in 2012.
A 2009 version of the agreement would have resulted in the relocation of 9,000 Marines to Guam, but that plan was downsized after the military acknowledged in an impact study the magnitude would be too great for Guam to handle.
Inada's visit to Guam last week followed US Secretary of Defense Ash Carter's meeting with the minister in Tokyo last month.