Japan on Friday vowed it would respond to "any scenario" after a threat by North Korea that Tokyo would be "consumed in nuclear flames".
"We are aware of the remarks made by North Korea, through the media and other channels. We cannot comment on our reaction to the remarks for operational reasons," a defence ministry official told AFP.
"All we can say is we will take every possible measure to respond to any scenario."
Japan, the only country ever to have suffered a nuclear attack, has authorised its armed forces to shoot down any North Korean missile headed towards its territory.
This week Patriot missile batteries were stationed around Tokyo to protect the 30 million people who live there.
In addition to the Patriots, Aegis destroyers equipped with sea-based interceptor missiles have been deployed in the Sea of Japan (East Sea) and on Friday the government said it would be permanently installing missile defences in Okinawa.
Tokyo's comments came after the Korean Central News Agency said any attempt to shoot down its missile would result in war.
"Japan is always in the cross-hairs of our revolutionary army and if Japan makes a slightest move, the spark of war will touch Japan first," KCNA said in a commentary.
"Japan must come to its senses and behave rightly," it added.