Government officials did not immediately confirm the reports, but authorities in one town told AFP they were suspending a drill planned for next week on orders from Tokyo.
The decision comes after US President Donald Trump and North Korea's leader Kim Jong Un met last week in Singapore, with the pair signing a joint document calling for denuclearisation of the Korean peninsula.
But the city suddenly cancelled all preparations late Wednesday after being instructed by the government that "drills should be postponed for the time being following a change in the environment after the US-North Korea summit," he said.
Last year, Pyongyang fired two missiles over Japan and it has splashed others into the sea near the country, sparking a mix of panic and outrage.
But the regional mood has turned towards diplomacy since the Winter Olympics hosted by South Korea, which set off a series of diplomatic moves culminating in the Trump-Kim meet.
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)