"As North Korea keeps making provocative comments, Japan, co-operating with relevant countries, will do what we have to do.
"For the moment, the most important thing is to implement sanctions under the UN Security Council resolutions."
PAC-3 batteries will also be installed in the semi-tropical island chain of Okinawa, Onodera told a television program broadcast on Monday.
He said Okinawa was "the place that is most effective in responding to emergencies ... so we should deploy the unit in Okinawa on a permanent basis".
Japan's armed forces are authorised to shoot down any North Korean missile headed towards its territory, a defence ministry spokesman said.
Intelligence reports suggest Pyongyang has readied two mid-range missiles on mobile launchers on its east coast and plans a test-firing before the April 15 birthday of late founding leader Kim Il-Sung.
- AFP