SEOUL (AFP) - North Korea fired a sixth short-range missile into the Sea of Japan on Monday, defying warnings from UN chief Ban Ki Moon and South Korea after a flurry of similar tests at the weekend.

The latest firing was confirmed by the South's Joint Chiefs of Staff (JCS), who said it was unclear if the North was testing guided missiles or rockets from multiple launchers.

"North Korea launched two projectiles on Monday - one in the morning and the other in the afternoon," a JCS spokesman told AFP.

Such drills are not unusual but they come as the Korean peninsula is only just emerging from a period of particularly elevated military tensions triggered by the North's nuclear test in February.

In a statement on Monday, Pyongyang angrily rejected criticism that the missile exercises were a deliberate attempt to kick off a fresh cycle of tensions.

"Military training ... is the indisputable right of any sovereign nation," the North's Committee for the Peaceful Reunification of Korea said.

"Viciously taking issue with our military's rocket firing training ... is an unacceptable challenge and a wanton provocation," it said.

North Korea fired three short-range guided missiles off its east coast on Saturday and another on Sunday.

South Korea had labelled the weekend tests "deplorable", while UN chief Ban Ki Moon has urged Pyongyang to exercise restraint.

"It is time for them to resume dialogue and lower the tensions," Ban said in Moscow on Sunday.

North Korea argues that the real provocation is coming from South Korea and the United States, which have carried out a series of small and large-scale joint military drills in recent months.

The joint exercises have included the use of nuclear-capable B2 stealth bombers and, most recently, the participation of the nuclear-powered aircraft carrier USS Nimitz.

On Monday South Korea's President Park Geun Hye's top security advisor, Kim Jang Soo, again urged Pyongyang to desist from any more drills.

"Whether it's just a test or a show of force, the North should not get involved in actions that create tension," Mr Kim said.

At one point, North Korea had been primed to test a pair of medium-range missiles, but US intelligence said the weapons were removed from their launch pads in early May.