North Koreans sign up to join the army in the midst of political tension with South Korea, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang August 23, 2015. Top aides to the leaders of North and South Korea resumed talks on Sunday after negotiating through the night in a bid to ease tensions involving an exchange of artillery fire that brought the peninsula to the brink of armed conflict. (Photo by Reuters/KCNA)

North Koreans sign up to join the army in the midst of political tension with South Korea, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang August 23, 2015. (Photo by Reuters/KCNA)

North Koreans who signed up to join the army train in the midst of political tension with South Korea, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang August 23, 2015. (Photo by Reuters/KCNA)

North Koreans who signed up to join the army march in the midst of political tension with South Korea, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang August 23, 2015. (Photo by Reuters/KCNA)

South Korean army's Multiple Launch Rocket System (MLRS) are deployed just south of the demilitarized zone separating the two Koreas in Yeoncheon, South Korea, August 23, 2015. (Photo by Shin Wong-su/Reuters/News1)

South Korean marines patrol along a bank of a shore on Yeonpyeong island just south of Northern Limit Line (NLL), South Korea, August 23, 2015. (Photo by Shin Wong-su/Reuters/News1)

South Korean marines patrol along a bank of a shore on Yeonpyeong island just south of Northern Limit Line (NLL), South Korea, August 23, 2015. (Photo by Min Gyeong-seok/Reuters/News1)

A South Korean army's Multiple Launch Rocket System (MLRS) (R) is deployed just south of the demilitarized zone separating the two Koreas in Yeoncheon, South Korea, August 23, 2015. (Photo by Lim Byung-sik/Reuters/Yonhap)

A man sits under a propaganda banner in Pyongyang, North Korea, Sunday, August 23, 2015. North and South Korea on Sunday resumed a second round of talks that temporarily pushed aside vows of imminent war on the peninsula. (Photo by Dita Alangkara/AP Photo)

South Korean amy soldiers walk on Unification Bridge, which leads to the demilitarized zone, near the border village of Panmunjom in Paju, South Korea, Sunday, August 23, 2015. South Korean and North Korean officials have resumed the second round of their high-level talks in the border village of Panmunjom on Sunday afternoon in an effort to ease mutual tension, South Korea's presidential office said. (Photo by Ahn Young-joon/AP Photo)

South Korean amy soldiers conduct their military exercise in Yeoncheon, south of the demilitarized zone that divides the two Koreas, South Korea, Sunday, August 23, 2015. (Photo by Ahn Young-joon/AP Photo)

South Korean army soldiers stand guard on Unification Bridge, which leads to the demilitarized zone, near the border village of Panmunjom in Paju, South Korea, Monday, August 24, 2015. (Photo by Ahn Young-joon/AP Photo)

South Korean army soldiers ride on a truck in Paju, south of the demilitarized zone that divides the two Koreas, South Korea, Monday, August 24, 2015. (Photo by Ahn Young-joon/AP Photo)

South Korean army soldiers ride on trucks in Paju, south of the demilitarized zone that divides the two Koreas, South Korea, Monday, August 24, 2015. Marathon negotiations by senior officials from the Koreas stretched into a third day on Monday as the rivals tried to pull back from the brink. South Korea's military, meanwhile, said North Korea continued to prepare for a fight, moving unusual numbers of troops, hovercraft and submarines to the border. (Photo by Ahn Young-joon/AP Photo)

South Korean soldiers ride a military truck on the road leading to the truce village of Panmunjom in the border city of Paju on August 24, 2015. Top-level North and South Korean negotiators talked through the night with no sign of an agreement on August 24 for ending a military standoff that has threatened to boil over into armed conflict. (Photo by AFP Photo/Yonhap)

A journalist stands next to a South Korean soldier standing guard as he waits for vehicles transporting a South Korean delegation at a checkpoint on the Grand Unification Bridge, which leads to the truce village Panmunjom, just south of the demilitarized zone separating the two Koreas, in Paju, South Korea, August 24, 2015. South Korean President Park Geun-hye talked tough on Monday, demanding that North Korea apologise over a recent landmine incident, even as the bitter rivals held marathon negotiations in a bid to defuse tensions that have brought the peninsula to the brink of armed conflict. (Photo by Kim Hong-Ji/Reuters)

Reporters prepare for a report at a checkpoint on the Grand Unification Bridge which leads to the truce village Panmunjom, just south of the demilitarized zone separating the two Koreas, in Paju, South Korea, August 24, 2015. (Photo by Kim Hong-Ji/Reuters)

A reporter prepares for a report at a checkpoint on the Grand Unification Bridge which leads to the truce village Panmunjom, just south of the demilitarized zone separating the two Koreas, in Paju, South Korea, August 24, 2015. (Photo by Kim Hong-Ji/Reuters)

Journalists wait for vehicles transporting South Korean delegation at a checkpoint on the Grand Unification Bridge which leads to the truce village Panmunjom, just south of the demilitarized zone separating the two Koreas, in Paju, South Korea, August 24, 2015. (Photo by Kim Hong-Ji/Reuters)

South Korean soldiers stand guard at a checkpoint on the Grand Unification Bridge which leads to the truce village Panmunjom, just south of the demilitarized zone separating the two Koreas, in Paju, South Korea, August 24, 2015. (Photo by Kim Hong-Ji/Reuters)

South Korean soldiers stand guard at a checkpoint on the Grand Unification Bridge which leads to the truce village Panmunjom, just south of the demilitarized zone separating the two Koreas, in Paju, South Korea, August 24, 2015. (Photo by Kim Hong-Ji/Reuters)

South Korean National Security Adviser Kim Kwan-jin (R), South Korean Unification Minister Hong Yong-pyo (2nd R), Secretary of the Central Committee of the Workers' Party of Korea Kim Yang Gon (2nd L), and Hwang Pyong-so (L), the top military aide to the North's leader Kim Jong Un, shake hands after the inter-Korean high-level talks at the truce village of Panmunjom inside the Demilitarized Zone separating the two Koreas, in this picture provided by the Unification Ministry and released by Yonhap on August 25, 2015. North and South Korea reached agreement early on Tuesday to end a standoff involving an exchange of artillery fire that had pushed the divided peninsula into a state of heightened military tension. (Photo by Reuters/Yonhap/The Unification Ministry)