|Residents of South Korea's Yeonpyeong island were moved to air-raid bunkers in anticipation of Monday's live-fire drill
South Korea has conducted a live-fire military drill in spite of rising tensions with the North that have prompted an emergency United Nations Security Council meeting.
Artillery fire was heard by several witnesses on the South Korean island of Yeonpyeong on Monday.
Residents of Yeonpyeong island, which lies in disputed waters off the Korean peninsula's west coast, were ordered to move into air-raid bunkers before the military exercise, according to South Korean media.
Sebastian Walker reports on the move to the bunkers on Yeonpyeong Island
North Korea had threatened to strike if the South went ahead with the military drill.
Four South Koreans were killed on Yeonpyeong last month when the North shelled part of the island.
Al Jazeera's Steve Chao, reporting from Incheon, a city on the country's western coast, said that the South Korean government denied that the exercise was a provocation, insisting that it was a routine drill.
But South Korea remains on high alert.
"We're also hearing initial reports that South Korea has scrambled F-15 fighter jets into the air," our correspondent said.
He said that South Korean residents living along the border with North Korea were moved in anticipation of an attack, and quoted the South Korean defence minister as declaring that air strikes would be used in the event of another North Korean attack.
Our correspondent earlier reported that the North Koreans view these drills as "proactive", saying: "There is even talk that North Korean jets have been taken out of their hangers - possibly along the west coast in a possible attempt to launch an attack in the event that these drills go forward."
Christine Ahn, a policy analyst at the Korea Policy Institute in California, told Al Jazeera that the threat of war with North Korea is very real.
"North Korea has said that they would respond with even more force than the November 23 retaliation on Yeonpyeong," she said.
"So I would say that if the South Koreans are in fact starting the live fire that I think we should expect a North Korea retaliation.
"And, unfortunately, that's going to draw in both the United States, and potentially China, into a larger conflict that nobody wants ... I think that the leaders of the United States and South Korea are now playing a very dangerous game that could really escalate into a full-blown war."
Al Jazeera's Melissa Chan, reporting from Beijing, said that the Chinese government there had not yet issued an official response to the South Korean drill.
"But they knew that the South Koreans were planning these military exercises, and the message from China has been, over the past week, 'Everyone stay calm, and let's try to have some restraint over the situation'," she said.
"Certainly the Chinese have been very worried about the escalation of the situation over the past month, and their strategy has really been to push for the status quo, to try to get everyone to talk.
"But, of course, the South Korean-Chinese relationship has been at a pretty good low as a result of all that has happened, with the perception among the South Koreans that the Chinese are not being proactive enough in handling and dealing with the situation."
The developments on the Korean peninsula came just hours after the UN Security Council met but failed to agree on a statement.
The 15-member bloc was split over whether to publicly blame North Korea for touching off the crisis, with China, North Korea's staunchest supporter on the council, and Russia rejecting the idea of assigning blame to Pyongyang.
The US and Japan have said that they will back South Korea in the event of a war with North Korea.
Following Sunday's Security Council meeting, Vitaly Churkin, Russia's UN envoy, called for South Korea to halt its planned military exercises.
"It's better to refrain from doing this exercise at this point in time," he said.
Susan Rice, the US ambassador to the UN, said the impasse was unlikely to be bridged.
The Reuters news agency reported diplomats as saying that a Russian draft statement called on both sides to exercise "maximum restraint" while a British draft statement had the Security Council saying it "deplores" North Korea's latest actions.
US and Chinese officials have described the situation on the Korean Peninsula as "extremely precarious" and a "tinderbox".
But China has blocked recent Western attempts to get the Security Council to rebuke Pyongyang over the deadly artillery shelling of Yeonpyeong and the North's nuclear activities.
The UN Secretariat distributed to council members a document on an investigation into the November 23 incident by the so-called UN Command, the US-led military forces in South Korea that monitor compliance with the 1953 Armistice Agreement that ended the Korean War.
That probe concluded the South did not violate the armistice with its November 23 military drills in disputed waters, while the North committed a "deliberate and premeditated attack" that was a "serious violation" of the cease-fire, according to the document, the Reuters news agency reported.