SEOUL (AFP) – South Korea deployed rocket launchers and extra artillery on a frontline border island bombarded last week by North Korea, as Seoul’s leader vowed Monday to make Pyongyang pay for any fresh provocations.

An AFP photographer saw extra soldiers on the island and multiple rocket launchers being installed, six days after the barrage which triggered fury in the South and alarm worldwide.

Military officials quoted by Yonhap news agency said the number of K-9 self-propelled howitzers there had been doubled to 12.

Officials in a loudspeaker broadcast also announced plans for a live-fire drill Tuesday and told residents to shelter in bunkers. But hours later, another broadcast announced there would be no such drill and blamed “wrong information”.

The drill had been planned but was delayed, a military official told Yonhap news agency on condition of anonymity. The reason was unclear.

President Lee Myung-Bak, under fire for the military’s perceived feeble response to last Tuesday’s attack which killed two civilians and two marines, indicated Seoul would not make the same mistake twice.

“If the North commits any additional provocations against the South, we will make sure that it pays a dear price without fail,” the grim-faced leader said in a nationally televised address, calling the shelling “a crime against humanity”.

Lee made no mention of China’s call for talks to end the crisis, in what one analyst saw as a tacit dismissal of it. Instead, he highlighted Pyongyang’s past deadly attacks.

The South realises the North will not on its own abandon its nuclear programme or brinkmanship policy, he said, adding that tolerance would “spawn nothing but more serious provocations”.

The US ambassador to the United Nations on Monday urged tighter enforcement of sanctions against North Korea and called on China to play a “responsible leadership role” in defusing the crisis.

Speaking at the UN, Susan Rice also vowed that the United States will “confront the threat” posed by North Korea.

Her comments came hours after the United States and South Korea staged the second day of their biggest-ever naval exercise, a show of strength against the regime that has tested nuclear bombs and is blamed for sinking a South Korean warship in March.

The sinking killed 46 sailors and sharply raised tensions, but the deadly artillery attack — which also wounded 18 people and set homes and hillsides ablaze — was the first on civilian areas in the South since the 1950-1953 war.

Such a provocation was unprecedented, Lee said.

“A military attack against civilians is strictly prohibited even in time of war; it is a crime against humanity,” he said.

Lee said a school was holding classes only a few metres (yards) from where shells landed, adding: “I am outraged by the ruthlessness of the North Korean regime, which is even indifferent to the lives of little children.”

The government has vowed to strengthen defences on all five border islands.

Legislators said the military is seeking 312 billion won (270 million dollars) in next year’s budget to bolster weaponry.

Far to the south of the disputed border, US and South Korean fleets staged an intensive live-fire exercise involving multiple aircraft from the US carrier George Washington.

Eleven ships plus aircraft and more than 7,000 personnel are taking part in the four-day drill which began Sunday.

Pyongyang said the naval exercise brings the peninsula to the brink of war. The drill has also riled China, which sees the Yellow Sea as its backyard.

But China, the North’s sole major ally, has itself angered South Koreans by failing to join international condemnation of its neighbour.

China called Sunday for emergency consultations between chief envoys to the stalled six-nation talks on the North’s nuclear disarmament.

The United States had no immediate reaction, but Japan was reluctant.

Chief Cabinet Secretary Yoshito Sengoku said Japan cannot be “positive towards consultations” unless the North seriously faces the implications of its attack on South Korean civilians and its nuclear development.

The other members of the six-party forum are Russia and the North itself.

Lee’s tougher tone chimes with the public mood, according to an opinion poll which found increasing support for a harder line against Pyongyang.