Veteran US troubleshooter Bill Richardson arrived Thursday in North Korea, saying he hoped he could "make a difference" as Seoul announced plans for a live-fire drill on a key frontline island.

Richardson's visit comes less than a month after the North sparked global alarm and inflamed regional tensions with its deadly shelling of the South's Yeonpyeong island and revelations of an extensive uranium enrichment programme.

South Korea on Thursday announced a major reshuffle of its military aimed to boost the strength of its defences against the North, after fierce domestic criticism that its response to the November 23 attack was weak.

"We are heading to North Korea in hopes of bringing peace. My message is that we need to persuade them to stop some of the aggressive actions that North Korea has taken," Richardson told reporters at Beijing's airport.

"I hope I can help out. I hope I can make a difference."

Richardson, the New Mexico governor and a former US ambassador to the United Nations, who has travelled to North Korea several times in the past, arrived in Pyongyang later in the day, Chinese state media said.

He was due back in China on Monday.

While Richardson was en route to the North, Seoul's military said it would stage a live-fire artillery exercise on Yeonpyeong island some time between December 18 and 21, depending on weather and "other relevant conditions".

It will be the first exercise of its kind on the island since the attack.

The US-led United Nations Command, which supervises the armistice that ended the 1950-53 war, said about 20 US soldiers would attend the drill to provide medical and communications services and assist in intelligence analysis.

The South Korean military said guns during the upcoming drill would be aimed away from the North as usual.

"We will react firmly and strongly to any fresh North Korean provocations," Lee Boong-Woo, spokesman for the South's Joint Chiefs of Staff, told a briefing.

Richardson -- who was invited to North Korea by Kim Kye-Gwan, North Korea's chief nuclear negotiator -- said he hoped Pyongyang would help tamp down mounting tensions.

"Whenever the North Koreans contact me, they always want to send a message of some kind. My hope is that they provide messages that can lessen tensions on the Korean peninsula," he told reporters.

"Some kind of negotiations need to take place. We will explore what makes sense," he added, noting that he also hoped to convince Pyongyang to honour its previous commitments to abandon its nuclear drive in six-nation disarmament talks.

Richardson said he hoped to visit the country's main nuclear complex at Yongbyon, where the North is apparently building a new reactor.

South Korea's Chosun Ilbo newspaper, quoting intelligence sources, reported Wednesday the North also had dug a tunnel more than 500 metres deep at its nuclear test site in possible preparation for a potential third test next year.

Richardson -- a former energy secretary in the administration of then US president Bill Clinton -- reiterated that his mission was a private one, and he was not an emissary of the administration of US President Barack Obama.

The veteran Democratic politician travelled twice to North Korea in the 1990s to secure the release of US prisoners and visited the country in April 2007 to bring back the remains of American servicemen killed in the Korean War.

Diplomats from countries involved in a six-nation effort to rid North Korea of its nuclear weapons capability have been touring the region to discuss a response to the shelling of Yeonpyeong island, which killed four people, including two civilians.

It was the first artillery attack on civilian-populated areas since the 1950-53 war.

A North Korean foreign ministry statement said the country was open to talks proposals but would not "beg".

"The DPRK supports all proposals for dialogue including the six-party talks, prompted by the desire to prevent a war and realise denuclearisation on the Korean Peninsula, but will never beg for it," said the statement, carried on the North's official news agency.

The South's defence ministry on Thursday announced promotions for 111 officers -- 75 from the army, 14 from the navy and 22 from the air force -- after it promised to retaliate with air strikes in the event of another attack.

China, the North's sole major ally, has called for emergency talks between members of the six-party forum on the North's nuclear disarmament.

But the United States, South Korea and Japan -- which have staged a series of military exercises in the region in recent weeks -- snubbed the offer, instead holding talks on their own earlier this month in Washington.

The South's nuclear envoy has ruled out talks with the North at present and called for greater international pressure on Pyongyang to stop its armed provocations, Yonhap news agency reported from Moscow.

US Deputy Secretary of State James Steinberg met with Chinese State Councillor Dai Bingguo, the country's most senior foreign policy-maker, on Thursday as part of a three-day visit to press for firmer action from Beijing in terms of reining in the North.