By Hongji Kim, Kyu-seok Shim and Joyce Lee
GIMPO, South Korea, Oct 26 (Reuters) - Tensions between North Korea and South Korea are running high this week after Pyongyang sent a letter to the UN Security Council, repeating accusations that Seoul fabricated a September landmine incident, and after North Korean howitzers were spotted close to the border.
A Reuters witness at an observatory in South Korea overlooking the heavily armed border on Monday saw three North Korean armoured vehicles positioned
in clear view near the frontier.
South Korea's Yonhap news agency on Monday identified three vehicles as self-propelled 122-mm howitzers, saying their deployment near the border marked a rare public display of such artillery.
The three North Korean armored vehicles had their gun barrels pointed south and Reuters also observed about 20 to 30 North Korean soldiers carrying out fencing work inside the Demilitarised Zone (DMZ).
"It is highly unusual (for North Korea) to expose its self-propelled artillery so conspicuously,” said Lim Eul-chul, a professor at Kyungnam University in Seoul.
"By deliberately displaying it, North Korea is signalling through action, not words, that it intends to enforce its border policy through force rather than dialogue or negotiation."
It is also warning South Korea to exercise caution about escalating border friction, aiming to prevent an accidental clash, he added.
North Korean state media KCNA reported that in the letter sent on Sunday, the country's UN representative said Seoul was using the landmine incident to depict Pyongyang's border construction as a military incursion.
North Korea warned in the letter that violations of its sovereignty could trigger self-defence measures and that South Korea would be "wholly accountable for all the ensuing consequences."
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The letter is a response to a South Korean letter to the Security Council last week, which said a September 21 blast in the DMZ was planted by North Korean troops and constituted a violation of the Korean War Armistice Agreement.
The UN Command, which oversees the DMZ, has said a North Korean mine across the line violated the armistice. Pyongyang has denied responsibility. The UN Command on Monday said it would not comment on specific military activities.
A spokesperson for South Korea's Unification Ministry said that the North Korean letter appears to repeat North Korea's existing position and seeks to justify its so-called border line marking work.
The ministry had no separate comment on the placement of the armoured vehicles. Seoul has proposed dialogue with North Korea to defuse border tensions.
North Korea's letter also repeated accusations that South Korea had opened fire on North Korean personnel, calling that a violation of the UN Charter, which bars the threat or use of force against another state's territorial integrity.
Seoul has said its military issues warning broadcasts and fires warning shots to send North Korean soldiers back across the line when they cross the military demarcation line (MDL), which bisects the DMZ.
North Korean troops have been building tactical roads and fences and laying mines near the MDL in recent years.
Yonhap also reported on Sunday that North Korean troops were conducting drills on the coast of Kaepung county, about 1.5 km (1 mile) from the observatory.
In 2015, there was a similar incident in which South Korean troops were injured by North Korean mines. Then, Seoul resumed anti-North Korea loudspeaker broadcasts across the DMZ, triggering a military standoff. After North Korea expressed regret, the standoff ended with a high-level inter-Korean agreement.
(Reporting by Kyu-seok Shim and Joyce Lee; Editing by Bill Berkrot and Edwina Gibbs)
