SEOUL - North Korea fired a volley of shots into the sea using multiple rocket launchers Tuesday, in an apparent show of force to coincide with South Korea-US joint military exercises, South Korean officials said.
Before noon, the North fired three shots using a multiple launch rocket system (MLRS), a high-mobility automatic launcher capable of firing surface-to-surface rockets, the South's Defence Ministry said.
The projectiles were launched from the North's eastern port of Wonsan and flew 55 kilometres (33 miles) into the Sea of Japan (East Sea), it said.
The North fired four more MLRS shots from 4:17pm (0717 GMT) that flew about 155 kilometres, the ministry said.
"North Korea is believed to have tested two different types of MLRS," a ministry spokesman told AFP.
South Korean troops have increased their vigilance following a series of North Korean missile launches that drew condemnation from South Korea and the United States.
North Korea test-fired four short-range Scud missiles off its east coast last week, followed by two more missiles on Monday.
South Korea called the missile launches a "reckless provocation", while the United States demanded the North show restraint and abide by UN Security Council resolutions.
The Scuds are at the longer edge of the short-range spectrum, with an estimated reach of 300-800 kilometres - capable of striking any target in the South.
It is not unusual for North Korea to carry out such tests, which often go unreported by South Korea.
But Washington said the latest missile tests breached UN resolutions that require Pyongyang to abandon its ballistic missile programme.
The missile tests have clearly been timed to coincide with annual South Korea-US military exercises that started a week ago and run until mid-April.
Pyongyang routinely condemns the South-US joint exercises as rehearsals for invasion.
Last year the drills coincided with a sharp and unusually protracted surge in military tensions that saw North Korea issuing apocalyptic threats of pre-emptive nuclear strikes.
By contrast, this year's drills began as relations between Seoul and Pyongyang were enjoying something of a thaw.
They overlapped with the end of the first reunion for more than three years of families divided by the Korean War - an event that raised hopes of greater cross-border cooperation.
Pyongyang had initially insisted that the joint exercises be postponed until after the reunions finished. But Seoul refused and - in a rare concession - the North allowed the family gatherings on its territory to go ahead as scheduled.
Analysts believe the missile tests reflect Pyongyang's need to flex its muscles in the wake of the reunion compromise.