North Korea test-fired three short-range missiles into the sea between Japan and the Korean peninsula this week, a report said on Friday.
The hermit state lobbed the missiles into the Sea of Japan (East Sea) on Wednesday, Japan's Sankei Shimbun newspaper quoted anonymous Japanese government sources as saying.
Outgoing Defence Minister Yasuo Ichikawa initially said he was 'aware' the missile tests had taken place, leaving his bureaucrats scrambling when he later said only that he had intended to convey he was aware of reports of the test.
The ministry said it was analysing intelligence and had put defence bodies on alert against provocative acts from the unpredictable regime, the Sankei reported.
In Seoul, the South Korean defence ministry and Joint Chiefs of Staff declined to confirm the report.
North Korea reportedly test-fired two short-range missiles off its east coast on December 19, the same day it announced the death of leader Kim Jong-Il.
The Sankei said the latest launch was believed to have been delayed because of the former leader's death.
The communist country has frequently conducted short-range missile tests in recent years. South Korean officials say they are part of routine exercises but the tests are sometimes timed to coincide with periods of tension.
Since Kim's death there has been speculation that his son and successor, Kim Jong-Un may try to burnish his military credentials by conducting missile tests.