Tensions have risen in the Korean Peninsula ahead of Sunday's planned joint military exercises by South Korea and the United States, with the North warning that the region was “inching closer to the brink of war”.

Sounds of artillery fire were heard on South Korea's Yeongpyeong Island on the Yellow Sea on Friday, the site of Tuesday's shelling by the North which left four people dead and at least 18 injured. The South Korean military said two explosions were heard, triggering fresh panic among residents, and it was verifying the source of the sounds.

Reports suggested the North was likely conducting artillery drills.

The North's official Korean Central News Agency (KCNA) warned in a statement on Friday “the situation on the Korean peninsula is inching closer to the brink of war”, and threatened another “shower of dreadful fire” if the South carried out any military provocations.

The warning came from the Democratic People's Republic of Korea (DPRK), as the North is officially known, even as the Lee Myung-bak administration in Seoul came under increasing pressure to respond to Tuesday's exchange of fire, which has been seen as possibly the most serious escalation in tensions since the end of the Korean War and the signing of an Armistice Agreement in 1953.

The North has blamed the South for starting the hostilities by holding live-ammunition sea drills and firing into its sea area. The South Korean military, however, said its drills were conducted in its territory in the disputed waters of the Yellow Sea west of the Korean Peninsula, and that its firing was westward, away from the land border with the North. The North Korean military responded by shelling the populated Yeongpyeong Island.

Mr. Lee's administration has come under fire for its slow response to the attack. On Thursday, Mr. Lee sacked Defence Minister Kim Tae, following criticism that the country's defences had been exposed by the attack. The former Joint Chiefs of Staff chairman, Kim Kwan-jin, was announced as his replacement on Friday. Mr. Lee also announced reinforcements for the 4,000-strong troop presence on five Yellow Sea islands.

The U.S., which has 28,000 troops in South Korea, has dispatched the aircraft carrier, USS George Washington, to the region.

China has voiced concerns over the move, saying it was opposed to the four-day military exercises scheduled to be conducted by the U.S. and South Korea starting on Sunday.

“We hold a consistent and clear-cut stance on the issue. We oppose any party to take any military acts in our exclusive economic zone without permission,” Foreign Ministry spokesperson Hong Lei said in a statement on Friday. “As the Korean Peninsula situation is highly complicated and sensitive, all parties concerned should stay calm and exercise restraint.”

While China has, in the past, strongly hit out at the U.S. deploying its aircraft carriers in the Yellow Sea, Foreign Ministry spokesperson Hong Lei refused to directly criticise the U.S. at a briefing on Thursday. “We have expressed our concern,” he said. “Under the current circumstances, we hope relevant parties do more to contribute to regional peace and stability.”

While China, as the North's only major ally, has faced pressure to play a more influential role to rein in Pyongyang, officials and analysts here say Beijing's influence over the Kim Jong-il regime is limited. The latest round of tensions comes as the North Korean leader Kim Jong-il prepares for the succession of his 26 year-old son Kim Jong-un, about whom little is known. The two Kims are on an “inspection tour” of the North along with the country's top military officials. The official KCNA said they had visited a fish farm in Yongyon in southern Hwanghae province.

South Korean media reported that Yongyon was only a few kilometres from the artillery base from where Tuesday's shelling of Yeongpyeong was launched, and it was likely that Mr. Kim and his son had personally ordered the attack.

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