South Korea has called on North Korea to stop "provocative" and potentially dangerous rocket and missile tests, a day after Pyongyang test-fired 25 projectiles into the sea.

The rockets were fired into the Sea of Japan, the latest in a series of launches that have sparked criticism from Seoul and the US.

A South Korean ministry spokesman said on Sunday 10 rockets were fired at 6:20 pm local time and eight more at 8:03 pm. Another seven followed, the last at 9:30 pm.

Seoul's military "has maintained a close watch for possible North Korean provocations", the spokesman said.

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-US military exercises that started in February and will run until mid-April.

Pyongyang routinely condemns the exercises as rehearsals for an invasion, while Seoul and Washington say they are purely defensive.

South Korea has called the North's launches a "reckless provocation" while Washington urged Pyongyang to halt the tests immediately, saying they risked inflaming regional tensions.

"We urge North Korea to stop provocative activities that will heighten military tension across the border," the spokesman said.

The North has defended its missile and rocket tests as justifiable self-defence drills.

Nuclear threats

Sunday's rocket launch comes two days after North Korea's National Defence Commission threatened to demonstrate its nuclear deterrence.

"Additional measures will be taken to demonstrate its might one after another as long as the US nuclear threat and blackmail persist as now", the commission said in a statement.

"The US 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."

North Korea and its main ally China want a resumption of six-party talks on the North's nuclear weapons programme.

But the United States and South Korea both insist that Pyongyang first demonstrate some tangible commitment to abandoning nuclear weapons.

The North carried out nuclear tests in 2006, 2009 and in February last year.

Despite tensions over the drills and the North's missile tests, cross-border ties are currently enjoying an upswing.

The two Koreas recently held the first reunion for more than three years of families divided by the Korean War in an event that raised hopes of greater cooperation.

AFP