South Korea ordered civilians on five border islands to take shelter ahead of a live-fire exercise Monday despite North Korean threats of deadly retaliation.

VIDEO - North Korea\'s military threatened Friday to strike back if South Korea goes ahead with a planned live-fire drill on a border island which the communist state shelled last month. Images of South Korean marines patrolling Yeonpyong island.

The drill loomed as UN efforts to calm the peninsula\'s worst tensions in years failed, following a North Korean artillery bombardment of the South Korean island of Yeonpyeong last month.

The military said civilians on the five islands near the disputed Yellow Sea border with the North -- including Yeonpyeong, where the live-fire exercise was to take place -- were ordered to take shelter.

"It will happen today," a defence ministry spokesman told AFP, without giving a time for the planned firing.

Officials on Yeonpyeong made a similar loudspeaker announcement Monday morning, an AFP photographer said. They later told residents, reporters, officials and others on the island to move to shelters within 30 minutes.

Yonhap news agency, quoting sources, said the drill was expected to be held between 11:00 am and noon (0200-0300 GMT).

It said that apart from the military there were about 280 people on the island, which is 12 kilometres (seven miles) from the North Korean coast.

After a similar exercise by marines based on Yeonpyeong on November 23, the North fired some 170 shells onto or around the island, killing four people including civilians and damaging dozens of homes.

It has threatened even deadlier retaliation if the upcoming drill goes ahead.

The United Nations Security Council met to try to ease tensions but failed to reach agreement on a statement, Russia\'s UN envoy Vitaly Churkin said.

China rejected demands by Western nations that its ally North Korea be publicly condemned for last month\'s attack on Yeonpyeong, diplomats said.

Churkin said there had been no agreement on a joint statement and US ambassador Susan Rice said it was "safe to predict that the gaps that remain are unlikely to bridged".

The foreign ministers of China and Russia held telephone talks Saturday and urged South Korea to cancel its military exercise.

The North disputes the Yellow Sea border between the two Koreas drawn by United Nations forces after the 1950-53 war. It claims the waters around Yeonpyeong and other frontline islands as its own maritime territory.

The North says it attacked last month after the South\'s drill dropped shells into its waters.

On Saturday it said the upcoming exercise "would make it impossible to prevent the situation on the Korean peninsula from exploding and escape its ensuing disaster".

Pyongyang said its military has already threatened "decisive and merciless punishment" for such an action and "does not make an empty talk".

Last month\'s bombardment was the first of civilian areas in the South since the Korean War. It sparked outrage in the South, which rushed more troops and guns to the frontline islands.

The South says the live-fire drill is a routine defensive exercise, with its artillery firing into the sea off the southwest coast and away from North Korea.

Representatives of the United Nations Command, which supervises the armistice in place since the 1950-53 war, were scheduled to observe it.

Some 20 US soldiers, part of the 28,500 US troops based in the South, were scheduled to play supporting roles. The North has derided them as a "human shield".

South Korea, heavily criticised for a perceived weak response to last month\'s bombardment, has vowed to hit back hard with air power against any new attack.

The Yellow Sea border has been a flashpoint for many years and was the scene of deadly naval clashes in 1999, 2002 and November 2009.

In March this year a South Korean corvette sank near the border with the loss of 46 lives. The South said a North Korean torpedo downed the ship, a charge denied by Pyongyang.