South Korean President Lee Myung-Bak called Monday for national unity in the face of North Korean attacks, saying the communist state would exploit divisions to strike again.

Lee, in a fortnightly radio address, also told South Koreans not to fear war with what he called the world's "most belligerent regime", even though Seoul's hope is for peace.

The South has staged a series of military exercises, including one with the United States, since the North shelled an island near the disputed Yellow Sea border last month and killed four people, including two civilians.

The North's ruling communist party newspaper branded the exercises a "dangerous collusion" between Seoul and Washington that would lead to "destruction".

"But our patience is limited," said Rodong Sinmun, denouncing Seoul as a "coward" for relying on Washington for military protection. The United States stations some 28,500 troops south of the border.

The North's artillery attack -- the first on a civilian area in the South since their 1950-53 conflict -- sparked fears of war.

But tensions have been high since May, when a South Korean-led multinational investigation concluded that a North Korean torpedo had sunk one of Seoul's warships two months earlier.

The North vehemently denied responsibility for the warship attack, and the investigation's findings were questioned by some in the South.

Lee said those disagreements, due to "ideological lines and political interests", had emboldened the North to stage the island attack.

"Seeing this, the North Koreans must have thought that their attacks could cause divisiveness in the South and that they might be able to get away with another provocation," he said.

"They are focusing on trying to pull us apart... If we show the North Koreans how steadfastly united we are, they will not dare challenge us."

Last month's artillery bombardment sparked widespread public anger. More than 80 percent of South Koreans believe their military should have hit back harder after the bombardment, according to a poll a week after the attack.

Lee cited a change of mood, saying applications to join the marine corps had doubled after the shelling.

The North accuses the South of provoking its November 23 bombardment of Yeonpyeong island by holding a firing drill there.

The South on December 20 staged another drill on Yeonpyeong but the North did not follow through with threats of a new and deadlier attack.

On Thursday last week, in another show of strength, Seoul deployed tanks, artillery and jet fighters in a live-fire exercise on the mainland.

The military said Sunday it would stage more firing drills this week, but not near the disputed sea border, describing them as routine training. A defence ministry spokesman said one of the drills was held Monday.

The North's KCNA news agency said the drills this week would drive the situation "to the brink of a war".

Lee called again for a strong response to any future attacks.

"We have now been awakened to the realisation that war can be prevented and peace assured only when such provocations are met with a strong response," the president said. "Fear of war is never helpful in preventing war."

Analysts along with US and South Korean government officials say the Yeonpyeong attack was likely linked to preparations for a power transfer in the North.

They say the aim is to present Kim Jong-Un, youngest son and heir apparent to Kim Jong-Il, as a tough and resolute leader and to create a warlike atmosphere to inspire unity.

A Seoul-based radio station which broadcasts to the North said Monday a train carrying birthday gifts for Jong-Un derailed this month in a possible act of sabotage.

Open Radio for North Korea said the train derailed upon departing from Sinuiju, on the border with China, on December 11.

It quoted a North Korean military intelligence official as saying sabotage by regime opponents may have caused the crash. The South's National Intelligence Service said it was checking the report.

earlier related report
South Korea, China defense chiefs to meet
Seoul (UPI) Dec 27, 2010 - South Korea likely will press China to rein in North Korea's military when South Korean and Chinese defense ministers meet in February.

"Defense Minister Kim Kwan-jin will meet with his Chinese counterpart Liang Guanglie in Beijing during February," a South Korean defense ministry official said. "Working-level officials will meet in January to set the agenda for the meeting."

Announcement of the meeting comes amid rising tensions on the Korean Peninsula since North Korea unexpectedly shelled the South Korean island of Yeonpyeong in mid November.

The daylight attack, in which North Korea fired around 170 shells, damaged dozens of house and several military buildings. It also killed two South Korean marines and two civilians and injured at least 20 people. South Korean forces returned fire with 155mm K-9 self-propelled howitzers.

The last meeting between Chinese and South Korean defense officials was in May 2009. No date has been set for the meeting in February.

The official said Seoul and Beijing have been working on another meeting. But finalization of dates was delayed by North Korea's shelling of Yeonpyeong Island and the subsequent resignation of South Korean Defense Minister Kim Tae-young. He stepped down amid assertions that the military was caught unaware of a North Korean threat and was slow to respond to the North's attack.

South Korean President Lee Myung-bak accepted the minister's resignation "to improve the atmosphere in the military and to handle the series of incidents," a presidential official said at the time.

The North Korean attack was condemned by many of South Korea's allies, including the United States. Washington repeatedly urged China to do more to pressure its ally North Korea not to ramp up military tensions between the two Koreas officially still at war since the 1953 cease-fire agreement that split the peninsula into two countries.

The shelling is believed to have been in response to South Korean military exercises in the politically sensitive sea area where the main Yeonpyeong Island is less than 8 miles from the North Korean mainland.

Yeonpyeong lies near the Northern Limit Line, the sea boundary agreed to by both Koreas in the 1953 Armistice that ended three years war. But North Korea increasingly has contested the agreement in the past 15 years.

South Korea is widely expected to ask China to "act responsibly" in order to stem North Korea's additional provocations against the South.

"The defense ministers will likely exchange views on the North Korean attack and Pyongyang's torpedoing of a South Korean naval vessel, though the meeting will focus on promoting bilateral defense cooperation and peace in Northeast Asia," another ministry official said.

The Yeonpyeong Island attack and the March sinking of a South Korean naval patrol vessel, which killed 46 sailors, have left relations between the two Koreas at their worst for several years.

An international investigating team said it found strong evidence that the 1,200-ton Cheonan was split in half by a torpedo of North Korean manufacture. The team said the torpedo was likely fired by a small to mid-size submarine.

North Korea's National Defense Commission denied it had anything to do with the attack on the Cheonan.

The deteriorating inter-Korean relationship has resulted in more military drills and live-firing exercises by South Korea close to its borders with North Korea, including on Yeonpyeong Island, as well as sea exercises with its ally the United States in the Yellow Sea.

Little hope of improved Korean relations appears on the horizon, the Seoul think tank Institute for National Security Strategy said. North Korea is likely to be more hostile because military leaders will compete military actions against the South to impress the country's leader-in-waiting Kim Jong Un, 28.

Kim Jong Un, son of leader Kim Jong Il, will further consolidate his power by becoming a vice head of the National Defense Commission, of which his father is chairman.

North Korea will "strive to increase special forces and develop strategies for dominance in limited conflicts against South Korea," the INSS said. That could mean the North attacks vessels, front-line observation posts and defectors living in South Korea.