Japan is always gathering and analysing information on North Korea 's nuclear missile situation with great interest, its top government spokesman said on Tuesday.

Chief Cabinet Secretary Yoshihide Suga told a news conference that the government was taking all possible measures for warning and surveillance of North Korea .

North Korea declared on Sunday it could test-launch an intercontinental ballistic missile (ICBM) at any time from any location set by leader Kim Jong Un, saying a hostile U.S. policy was to blame for its arms development.