South Korean troops geared up today for artillery drills on a border island shelled by North Korea last month despite Pyongyang's threat to retaliate again, as Russia and China expressed concerns over rising tensions on the divided peninsula.

The North warned yesterday that it would strike even harder than before if the South went ahead with its planned drills. Four people died last month in the North's attack on Yeonpyeong Island near the tense sea border.

The US supports South Korea, saying the country has a right to conduct such a military exercise. However, Russia's Foreign Ministry expressed its "extreme concern" yesterday over the drills and urged South Korea to cancel them to prevent a further escalation of tensions.

China, the North's key ally, also said it is firmly opposed to any acts that could worsen already-high tensions on the Korean peninsula. "In regard to what could lead to worsening the situation or any escalation of acts of sabotage of regional peace and stability, China is firmly and unambiguously opposed," Chinese Foreign Ministry spokeswoman Jiang Yu said in a statement today.

South Korea's Joint Chiefs of Staff said today that marines would go ahead with the drills as scheduled and that the military was ready to respond to any possible provocation.

"We have a right to conduct our own military drills," a Joint Chiefs of Staff officer said.

The North's threat and the Chinese and Russian concerns will not affect the timing of the exercise, said the officer, who spoke anonymously, citing department rules.

Foreign Ministry spokesman Kim Young-sun said the drills are defensive in nature and are not aimed at stoking regional tensions.

The artillery drills were not expected to be held over the weekend because of bad weather and will be conducted either Monday or Tuesday, the Joint Chiefs of Staff officer said.

Marines carrying rifles conducted routine patrols this morning on Yeonpyeong, and no warning for residents to evacuate to underground shelters had been issued. About 300 residents, officials and journalists remain on Yeonpyeong, but officials from Ongjin County, which governs the island, said they had no immediate plans to order a mandatory evacuation to the mainland.

"North Korea said it will deal the powerful ... blow at us if we go ahead and fire artillery. So residents are getting more restless," said Yoon Jin-young, a 48-year-old islander.

Activists launched balloons containing about 200,000 propaganda leaflets toward the North from the island, which is only about seven miles from North Korean shores. The balloons also carried 1,000 $1 bills and DVDs containing information on the North's artillery barrage last month.

Several bloody naval skirmishes occurred along the western sea border in recent years, but last month's assault was the first by the North to target a civilian area since the end of the 1950-53 Korean War. The North does not recognise the UN-drawn sea border in the area.