North, South Korea Trade Fire over Disputed Border

Tensions between North and South Korea are heating up again after Pyongyang announced it would conduct live-fire drills in the Yellow Sea.

North Korea fired about 100 shells into South Korean waters. Seoul responded by firing about 300 shells of its own back into South Korean sea territory.

The two countries exchanged fire over a disputed western sea border Monday, causing residents of South Korean islands to evacuate to shelters for hours.

Pyongyang has recently stepped up its threats against South Korea, protesting its joint military exercises with the United States.

North Korean officials call the war exercises, "an attempt to occupy Pyongyang" while South Korea and the United States say they're routine and defensive.

"This exercise was not designed to react to any political situation," said Paul Kennedy, commanding general of 3D Marine Expeditionary Brigade. "It is not designed to send a message. This is something that we have to do to be able to inter-operate with our allies."

The exercises, reported to be the biggest by the U.S. and South Korea since 1993, are scheduled to run until April 7.

On Sunday, Pyongyang threatened to conduct a fourth nuclear test aimed at improving its ability to attack mid- and long-range targets. The White House said North Koreas threats will only deepen its isolation.

Meanwhile, the country's sole ally in the region, China, is calling for both North and South Korea to show restraint.

"We hope all sides involved can remain calm and restrained," Hong Lei, Chinas Spokesman of Ministry and Foreign Affairs, said. "Refrain from taking actions that will heighten the tension and work together to preserve the Korean Peninsula's peace and stability."

Beijing traditionally sides with the United Nation in condemning provocative actions from the North, but they have fallen short of singling out North Korea, saying instead that both sides are responsible.