In pictures: Disputed inter-Korean western maritime border

The South Korean national flag flies from a boat on Baengnyeong Island on 15 June, 2010

The disputed western maritime border between North and South Korea is one of the region's major flashpoints.

The seafront of North Korea's west coast with signs reading "Long live Great leader Kim Il-Sung and his revolutionary ideology!", is seen from the South Korea-controlled island of Yeonpyeong near the disputed waters of the Yellow Sea on 14 April 2013

The Northern Limit Line (NLL) border was unilaterally drawn by the United Nations after the 1950-53 Korean War, as a line beyond which South Korean vessels were not to venture.

A South Korean military guard post is seen as a Navy MSB (Movement Sea Base) floats in the background at the South Korea-controlled island of Yeonpyeong near the disputed waters of the Yellow Sea on 13 April, 2013

North Korea disputes the border, however, saying the Military Demarcation Line much further south should be the true border.

A South Korean government ship sails by the Navy Movement Sea Base off the South Korea-controlled island of Yeonpyeong near the disputed waters of the Yellow Sea on 22 December 2010

There have been periodic skirmishes in the seas between North and South Korea, where fishing rights are hotly contested.

A resident gathers oyster as a South Korean Navy vessel floats in the background at the South Korea-controlled island of Yeonpyeong near the disputed waters of the Yellow Sea on 22 December, 2010

Five islands lie just to the south of the South Korean side of the NLL, including Baengnyeong and Yeonpyeong. The islands are home to tiny communities of fishermen and farmers.

A South Korean marine looks through binoculars on Baengnyeong Island on 15 June, 2010

Though they may be defensively ill-sited, the islands provide South Korea with a useful balcony from which to spy on the North Korean coast.

A giant floating crane lifts the stern of a South Korean warship to place it on a barge on 15 April, 2010

In March 2010, the border issue ignited when a South Korean navy warship sank near Baengnyeong Island, killing 46 sailors. Seoul says Pyongyang torpedoed the ship, but North Korea denies involvement.

A South Korean Marine officer salutes bronze statues of two marines that were put up during a ceremony to mark the first anniversary of North Korea's deadly shelling of Yeonpyeong island on 23 November, 2011 that left four South Koreans dead

Eight months later, North Korean shelling of Yeonpyeong Island left four South Koreans dead - two civilians and two marines.

South Korean marines patrol Yeonpyeong Island on 20 December 20, 2010

Following the attack, South Korea fortified its military presence on Yeonpyeong and other border islands.

In this photo provided by the Ongjin County, residents of Yeonpyeong Island rest as they evacuate from their homes to a shelter on the island, South Korea, near the West Sea border with North Korea on Monday, 31 March, 2014

In March 2014, cross-border firing forced residents of Baengnyeong Island into evacuation shelters. Seoul said it was responding to North Korean shelling - during a military exercise - which had fallen into South Korean territorial waters.

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