SEOUL, South Korea — North Korean soldiers boasted on state television they bombarded a front-line South Korean island with artillery last month as immediate retaliation after the South fired first.

The two Koreas have ramped up their rhetoric since the Nov. 23 attack killed four South Koreans on Yeonpyeong Island near their tense western sea border. North Korea has said it fired after South Korean shells landed in its waters, while the South has said its routine firing drill aimed away from the sea frontier and should not have provoked an attack.

North Korea’s war of words intensified around Friday’s 19th anniversary of leader Kim Jong Il’s appointment as the North’s supreme military commander. Kim’s military chief threatened last week to launch a "sacred" nuclear war against the South.

On Friday, North Korean soldiers appeared on a state TV program marking Kim’s appointment anniversary and bragged of participating in the artillery barrage.

"Our eyes were full of fire right after we saw the enemy’s shells being fired into our sacred waters," soldier Kim Moon Chol said, clinching his fists and standing shoulder-to-shoulder with three uniformed colleagues. Their ranks were unknown.

"At the order of ‘fire,’ we poured our merciless thunderbolt of fire at the enemy," he said in a loud, oratory-style speech.

A soldier whose uniform was full of military decorations expressed his loyalty to Kim Jong Il.

"Facing the enemy’s provocation, we shouted, ‘Let’s dedicate our lives to fighting the enemy and giving them a merciless death for our dear leader and supreme military commander,’" Kim Kyong Su said.

Their speeches constantly drew applause from the audience — mostly uniformed soldiers who spoke separately and vowed to get tougher with South Korea. They all later sang a military song together.

South Korea has staged a series of military drills — including one on Yeonpyeong Island on Dec. 20 — in a show of force against the North. The South’s President Lee Myung-bak, during a visit to front-line troops Thursday, said that South Korea must make "unsparing" retaliation if it suffers another surprise attack.

South Korea plans new routine naval firing exercises starting Monday, but not on Yeonpyeong and other border islands, according to the Defense Ministry.

The North’s state media said Sunday that the South’s Dec. 20 drills on Yeonpyeong showed its intention to fight North Korea to the end. "The warmongers should not misjudge the patience of" North Korea, the main Rodong Sinmun newspaper said in a commentary carried by the official Korean Central News Agency.

The state-run Institute for National Security Strategy in Seoul said in a report issued Sunday that the North may even directly invade Yeonpyeong and other Yellow Sea border islands next year, Yonhap news agency reported. Yonhap said the assessment linked the North’s belligerence to leader Kim’s moves to transfer power to his youngest son, but the report didn’t elaborate.

Calls to the institute were unanswered Sunday.

A report released Thursday by the Brussels-based International Crisis Group said that Koreas’ disputed maritime boundary and the volatility of North Korea’s internal politics have "created a serious risk that any further provocation might turn into a wider conflict." South Korea’s Institute of Foreign Affairs and National Security also said in a report last week that Pyongyang could be planning its third nuclear test next year.

Despite high tension, analyst Paik Hak-soon at the private Sejong Institute think tank near Seoul said North Korea probably won’t provoke the South again ahead of a planned summit between President Barack Obama and Chinese President Hu Jintao on Jan. 19.

Defense chiefs of South Korea and China are to meet in Beijing in February to discuss regional security issues.

South Korea, meanwhile, has decided not to resume calling North Korea its "main enemy" in a defense white paper to be issued in coming weeks, a Defense Ministry official said Sunday requesting anonymity citing department rules. He said South Korea will use a different description clearly showing North Korea is the enemy but gave no further details.

Conservatives have called on the Defense Ministry to restore the "main enemy" reference it had stopped using in 2004 amid then-warming ties with the North.

The two Koreas are still technically at war because their conflict in the early 1950s ended with an armistice, not a peace treaty. In recent years, several bloody naval skirmishes occurred near their disputed western sea border — drawn by the U.N. at the close of the Korean War.