Japanese officials have carried out exercises to see whether a missile defence shield could be deployed in the capital, Tokyo.
Teams set up radio masts and tested communications at two separate locations in the city.
The military was assessing whether Patriot Advanced Capability 3 (PAC-3) surface-to-air interceptor missiles could be deployed at such sites.
Concern over North Korea has prompted Japan to up its missile defence.
In 1998 Pyongyang test-fired a long-range Taepodong-1 missile over northern Japan.
In 2006 the communist state also tested a longer-range missile, as well as carrying out a nuclear test.
The Japanese military carried out their assessment in the capital overnight.
According to a military spokesman, the two sites surveyed were Shinjuku Park, a business hub in central Tokyo, and a site in Ichigaya, not far from the Imperial Palace and key government offices.
"We took surveys of buildings, which would be obstacles for the PAC-3, and conducted technical tests on communications," the spokesman said.
Other sites in the capital would also be investigated, he said.
PAC-3 missile defence systems have already been installed at two bases in Japan, with authorities planning an expansion to a total of 11 sites by 2011.
The Japanese government is also co-operating with the US on ship-based missile defence systems.
In December 2007, a Japanese warship successfully shot down a mock ballistic missile off Hawaii, in the first test of a system that will ultimately be installed on four destroyers.