North Korea fired four short-range missiles over the sea off its eastern coast on Thursday, a media official at South Korea's Defence Ministry said, but provided no information as to the purpose of the firing.
North Korea fired the missiles at 5:42 p.m. local time (0842 GMT) from a mountain site just north of the border with South Korea, the official said.
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Launches by the North of short-range missiles are not uncommon as part of military exercises.
The firing came days after the beginning of annual U.S. and South Korean joint military exercises, which the North routinely denounces as a preparation for war.
The North was angered this month when a nuclear-capable U.S. B-52 bomber made a sortie over South Korea, though the flight did not trigger a sharp escalation of military tension.
South Korea's Yonhap news agency said the missiles fired on Thursday were believed to be Scud short-range missiles, with a range of about 200 km (125 miles), which means they can hit targets in South Korea, but cannot reach Japan.
Also on Thursday, the South's YTN news channel reported that North Korea fired four missiles with an estimated range of 150-160 km on February 21.
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In Washington, Army Colonel Steven Warren, a Pentagon spokesman, said U.S. forces had monitored the North Korean launch of several Scud missiles.
Warren said the launch was evidently an unannounced weapons test, but the missiles did not appear to be targeting anything and landed off the country's east coast.
Asked if the United States considered the test provocative, Warren said: "This one actually we do not, frankly. We've seen these types of missile tests fairly regularly. It's a short-range Scud missile, which they are allowed to test. Nevertheless, we always call on the (North) Koreans to refrain from provocative actions."
Ties between the two Koreas are often fraught, but last week, hundreds of South Koreans crossed into the North to be reunited with family members they had not seen since the 1950-53 Korean War.
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The reunions, a rare show of cooperation between the two Koreas, were held despite North Korean anger over joint military exercises between South Korea and the United States. Last year, the exercises triggered weeks of North Korean threats of war.
On Monday, South Korea offered the North help with an outbreak of foot-and-mouth disease in pigs, which would be the first government-level humanitarian help since 2010.
Officials in Japan and China, were not immediately available for comment.