South Korea yesterday vowed to “punish the enemy” as hundreds of troops, fighter jets, tanks and attack helicopters prepared for massive new drills near the heavily armed border a month after a deadly North Korean artillery attack.

Although the North backed down from its threat to retaliate over South Korean drills on Monday in west coast waters claimed by both countries, South Korean forces have been on high alert this week, warning of surprise attacks.

The North responded to a November 23 artillery drill on South Korea’s front-line Yeonpyeong Island with an artillery bombardment that killed four, including two civilians.

The North has made some conciliatory gestures in recent days – telling a visiting US governor that it might allow international nuclear inspections of its atomic programmes – but Seoul appears unmoved and is bracing for possible aggression.

“We will completely punish the enemy if it provokes us again like the shelling of Yeonpyeong Island,” said Brig Gen Ju Eun-sik, chief of the army’s 1st armoured brigade.

South Korea’s navy began annual four-day firing and anti-submarine exercises yesterday off the country’s less-tense east coast.

The disputed western sea border has been the site of most of the Koreas’ recent military skirmishes, including last month’s artillery bombardment. But the east coast was used by the North as a submarine route for communist agents to infiltrate South Korea in the past.

South Korea’s army and air force also planned joint firing drills today near the Koreas’ land border.

The training – the 48th of its kind this year – will be the biggest-ever winter-time joint firing exercise that South Korea’s army and air force have staged, the army said in a statement. The drill will involve 800 troops, F-15K and KF-16 jet fighters, K-1 tanks, AH-1S attack helicopters and K-9 self-propelled guns, the statement said.