North Korea Sunday test-fired 18 rockets into the sea, South Korea's defence ministry said, the latest in a series of launches that have provoked criticism from Seoul and Washington.The rockets were fired off the North's east coast and flew about 70 kilometres (42 miles) over the Sea of Japan (East Sea), a ministry front man said.
The ministry said 10 rockets were fired at 6:20 pm (0920 GMT), and eight more at 8.03 pm.
Seoul's military "has maintained a close watch for possible North Korean provocations", the front man said.
Yonhap news agency earlier reported that 10 short-range missiles were fired.
South Korean troops have increased vigilance following a series of rocket or missile launches in late February and this month.
The activity coincides with annual South Korean-U.S. military exercises that started in February and will run until mid-April.
Pyongyang routinely condemns such war games as rehearsals for an invasion, while Seoul and Washington say they are purely defensive.
"We urge North Korea to stop provocative activities that will heighten military tension across the border," the front man said.
The North has defended its missile and rocket tests as justifiable self-defence drills.
South Korea has called the launches a "reckless provocation" while Washington urged Pyongyang to halt the tests immediately, saying they risked inflaming regional tensions.
Sunday's rocket launch came two days after the North's National Defence Commission threatened to demonstrate its nuclear deterrence.
Analysts said the comments could indicate the regime is preparing to carry out a fourth atomic test.
"Additional measures will be taken to demonstrate its might one after another as long as the U.S. nuclear threat and blackmail persist as now", the commission said in a statement.
"The U.S. had better roll back its worn-out hostile policy towards (North Korea) as soon as possible and shape a new realistic policy before it is too late."