SEOUL: North Korea flew an unmanned plane for surveillance or as a decoy after it fired a volley of shells near the disputed sea border with South Korea last week, an official said Tuesday.

The impoverished but nuclear-armed communist state has also aired rare footage of its new main battle tank, which was being closely analysed by South Korean authorities, a news agency report said.

"The North flew a drone, possibly for surveillance, after it fired artillery shells Monday last week into waters in the Yellow Sea," the military official was quoted as saying by a Joint Chiefs of Staff spokesman.

The North fired some 100 rounds from its coastline batteries into the sea shortly after the South ended a five-day naval exercise in the Yellow Sea.

"This seven-metre (23-foot)-wide drone hovered over the North`s waters, keeping a very low altitude, some 20 kilometres (13 miles) north of Yeonpyeong islands," the official said.

"It might be a surveillance drone or a decoy" aimed at disturbing the South`s radars and surveillance aircraft, he said.

It was the first time a North Korean drone had been spotted over the sensitive waters, the scene of deadly naval battles in the past decade.

Most recently, 46 sailors were killed in March when a South Korean warship was sunk near the disputed sea border.

Seoul accused the North of torpedoing the corvette and announced a series of military drills, alone or jointly with the Unites States, as a show of force.

Pyongyang denied responsibility and vowed to retaliate.

Yonhap news agency, meanwhile, said North Korea`s Chungang TV recently aired video footage of the country`s new main battle tank, called "Pokpung (Tiger Storm)."

Known as M2002, the new indigenous tank is thought to be based on the Soviet T-62 but equipped with a laser rangefinder, anti-aircraft machine guns and a modern fire control system.

On top of its fledgling nuclear arsenal, North Korea maintains huge conventional armed forces but South Korea`s military, backed by some 28,500 US troops, enjoys superiority in quality.

BDST: 1051 HRS, August 17, 2010