North Korea moves about 50 Soviet-era choppers to bases in Tartan and Nuchon, near the Yellow Sea, just three minutes from South Korea. The area was the scene of clashes between the two countries as far back as 1999.

Seoul (AsiaNews) - North Korea has recently deployed dozens of attack helicopters near its disputed sea border with South Korea, South Korean media reports said on Tuesday, as both sides strengthen their military presence in the area.

The North has posted at least 50 helicopters, Yonhap news agency said, citing unidentified Seoul officials, including upgraded versions of the North's Mi-2 helicopters as well as Mi-4 and Mi-8 models imported from the Soviet Union decades ago. Some are armed with machine guns and rockets.

"These choppers are being used for ground attacks and high-speed mobility forces exercises," Yonhap quoted an official as saying.

Helicopters from the two bases could reach the South's frontline island of Baengnyeong within two or three minutes.

The border saw deadly naval clashes in 1999, 2002 and 2009. In November 2010 the North shelled one of the South's five border islands, Yeonpyeong, and killed four South Koreans including two civilians.

Since then, Seoul has strengthened manpower and weaponry on the islands to forestall any new attack.

What is more, US and South Korean troops are set to stage an annual joint exercise next month (20-31 August) to improve their combat-readiness.

The drill would involve more than 30,000 US troops and more 50,000 South Korean soldiers.

North Korea has been told of the dates and of the non-provocative nature of the exercise, a government source said.

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