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By Choonsik Yoo
SEOUL Feb 27 (Reuters) - North Korea fired four short-range missiles over the sea off its east coast on Thursday, a media official at South Korea's Defence Ministry said, while providing no information on the purpose of the firing.
North Korea fired the missiles at 5:42 p.m. (0842 GMT) from a mountain site just north of the border with South Korea, the official said.
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 joint U.S. and South Korean military exercises which the North routinely denounces as 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.
The South'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 can not reach Japan.
Officials in Japan and North Korea's neighbour and only ally, China, were not available for comment.
South Korea's YTN news channel reported on Thursday that North Korea fired four missiles with an estimated range of 150 km - 160 km (93-100 miles) on Feb. 21.
Ties between the two Koreas are often fraught but this month, hundreds of South Koreans crossed into the North to be reunited with family members not seen since the 1950-53 Korean War.
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.
This week, South Korea offered North Korea help with an outbreak of foot-and-mouth disease in pigs, which would be the first government-level humanitarian help since 2010.
(Additional reporting by Ju-min Park and James Pearson; Editing by Robert Birsel)