North Korea threatens to launch two retaliatory strikes over further planned artillery drills on disputed island

Tense: South Korean marines patrol on Yeongpyeong Island as the country announced it would stage further artillery drills over the weekend

Stand off: South Korean Navy vessels lie off the disputed island. North Korea has threatened to launch two retaliatory strikes if the drills go ahead

North Korea has again warned its southern neighbour to stop planned artillery drills on disputed islands and said it would launch two retaliatory strikes if it failed to comply.

South Korea has said it plans to carry out a 24-hour live-fire drill on Yeonpyeong Island sometime between Saturday and Tuesday, depending on weather.

Pyongyang, which claims ownership of nearby waters and has said it considers the drills an infringement of its territory, responded to similar firing exercises last month by shelling the tiny island.

Patrol: Police officers walk past a shelter on the island. Artillery drills last month saw the north shell Yeonpyeong, killing four people

Envoy: New Mexico Governor Bill Richardson arrives in Pyongyang in a bid to ease the tension between the two countries

That attack killed four people on the island, including two civilians, which is home to a fishing community and military bases.

An unnamed senior North Korean military official told the Korean Central News Agency that if the south carried out more drills 'despite our military's prior warnings, second and third unpredictable self-defensive strikes will be made'.

A notice sent to the South Korean military today added that the retaliation would be made 'to safeguard our republic's sacred territorial waters' and that the 'intensity and scope of the strike will be more serious than the November 23 shelling'.

Seoul has said its planned drills are part of 'routine, justified' exercises and has warned that it is prepared to deal with any North Korean attack.

Representatives of the American-led UN Command, which oversees the armistice which ended the Korean War, will observe the drills.

The stand off comes as a high-profile U.S. state governor visited North Korea today in a bid to ease tensions.

New Mexico Governor Bill Richardson, who has been a frequent unofficial envoy for the north, said he wanted to visit the country's main nuclear complex and meet with senior officials during his four-day trip.

He said ahead of his visit that he expected to get some sort of message from North Korea.

'My objective is to see if we can reduce the tension in the Korean peninsula.'

State Department spokesman P.J. Crowley said the drills posed no threat.

'North Korea should not see these South Korean actions as a provocation,' he added.