Amphibious assault vehicles of the South Korean Marine Corps throw smoke bombs as they move to land on shore during a U.S.-South Korea joint landing operation drill in Pohang March 31, 2014. The drill is part of the two countries' annual military training called Foal Eagle, which began on February 24 and runs until April 18. North Korea declared a no-sail warning on Monday for areas off its west coast near a disputed border with South Korea and has notified the South that it will conduct firing drills, a South Korean government official said. The warning comes amid heightened tensions surrounding the North after the U.N. Security Council condemned Pyongyang for its mid-range missile launches last week, just as the leaders of South Korea, Japan and the United States met to discuss the North's arms programme. (Photo by Kim Hong-Ji/Reuters)

South Korean Marine amphibious assault vehicles land on the seashore during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. North Korea announced a live-fire drill on March 31 near its disputed maritime border with South Korea, further ratcheting up tensions a day after threatening a “new form” of nuclear test. (Photo by Jung Yeon-Je/AFP Photo)

US Marines take a positon during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. (Photo by Jung Yeon-Je/AFP Photo)

U.S. and South Korean marines participate in a U.S.-South Korea joint landing operation drill in Pohang March 31, 2014. (Photo by Kim Hong-Ji/Reuters)

US Marines get out from an amphibious assault vehicle during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. (Photo by Jung Yeon-Je/AFP Photo)

A journalist films as U.S. and South Korean marines participate in a U.S.-South Korea joint landing operation drill in Pohang March 31, 2014. (Photo by Kim Hong-Ji/Reuters)

South Korean and U.S. Marines participate in the U.S.-South Korea joint landing exercises called Ssangyong, part of the Foal Eagle military exercises, in Pohang, South Korea, Monday, March 31, 2014. (Photo by Jung Yeon-Je/AFP Photo)

An amphibious assault vehicle of the South Korean Marine Corps arrives on shore during a U.S.-South Korea joint landing operation drill in Pohang March 31, 2014. (Photo by Kim Hong-Ji/Reuters)

US Marines take a position during a joint landing operation by US and South Korean Marines in Pohang, 270 kms southeast of Seoul, on March 31, 2014. (Photo by Jung Yeon-Je/AFP Photo)

Amphibious assault vehicles of the South Korean Marine Corps throw smoke bombs as they move to land on shore during a U.S.-South Korea joint landing operation drill in Pohang March 31, 2014. (Photo by Kim Hong-Ji/Reuters)

Amphibious assault vehicles of the South Korean Marine Corps throw smoke bombs as they move to land on shore during a U.S.-South Korea joint landing operation drill in Pohang March 31, 2014. The drill is part of the two countries' annual military training called Foal Eagle, which began on February 24 and runs until April 18. (Photo by Kim Hong-Ji/Reuters)

U.S. marines participate in a U.S.-South Korea joint landing operation drill in Pohang March 31, 2014. (Photo by Kim Hong-Ji/Reuters)