SEOUL – North and South Korea exchanged artillery fire near their disputed sea border on Wednesday, highlighting instability along a heavily armed frontier for the second time in three months. North Korea warned the South that more rounds were on the way as a part of military training, and then fired off another barrage a few hours after delivering the message in a state media report. Analysts doubt the latest clash will escalate and see it more as an attempt by Pyongyang to stress tensions on the Korean peninsula and press home its demand for a peace deal that would open the way to international aid for its ruined economy. "No one can argue about the premeditated exercises staged by Korean People's Army units in waters of the North side," the North's KCNA news agency quoted the general staff of the country's army as saying. North Korea has more than 10,000 pieces of artillery aimed at the wealthy South and which could in a matter of hours destroy much of the capital Seoul, 25 miles from the border. South Korea's Joint Chiefs of Staff said the North fired artillery from land toward the South but landing on its side of the disputed sea border off the west coast. South Korea returned fire from its coastal artillery. "We want to express grave concern over the incident that resulted from the North's illegal act that unnecessarily creates tension through live-fire artillery fire," the South's Defense Ministry said in a message to the North.