Japan's Defence Minister Itsunori Onodera said his nation was on "high alert", with anti-missile defences deployed in Tokyo as a precaution.

BBC: South Korea raises alert with North to 'vital threat'

Earlier this week, Japan's Defence Minister Itsunori Onodera said a Chinese navy frigate close to the islands had locked its weapon-targeting radar on a Japanese navy ship on 30 January.

BBC: China rejects Japan radar-lock allegation

He named a close ally, Taku Yamasaki, as a new informal adviser, and appointed Yoshinori Ono, who wants to upgrade Japan's military, as the new minister for defence.

ECONOMIST: Japan