On Monday, Oct 12, North Korea launched five missiles off its east coast despite making a series of peace overtures since Aug 2009, the Yonhap agency reported.
"There have been indications that the North is getting ready to fire short-range missiles from the west coast," the source was quoted as saying.
The South Korean military did not confirm the information.
North Korea has barred shipping from part of the sea near its east and west coasts until Oct 20.
According to reports, the series of rocket tests was probably part of military exercises aimed at improving the country's rocket technology.