North Korea has shelled the South Korean border island of Yeonpyeong, killing two marines and injuring several others, prompting international condemnation. The North says the South fired on it first.
The shelling set buildings on fire and lasted about an hour
South Korean officials and media reports said on Tuesday that North Korean air force jets fired dozens of shells at the border island, setting buildings ablaze and injuring at least a dozen other people.
South Korean troops based on the island fired back, and the military was put on top alert, news agencies in the South reported.
North Korea, meanwhile, said the South had fired first; Seoul acknowledged it was conducting military operations close to the disputed maritime border between the two territories, but said it had been firing west, not north.
A senior South Korean defense ministry official, Lee Hong-ki, called the shelling "an intentional attack" and a "clear violation of the armistice" between the two countries.
South Korean President Lee Myung-bak said in response that his government was working to prevent the exchange of fire between the North and South. However, he added that his country would retaliate should the North attack again.
A defense ministry spokesman said that a Class-A military alert for battle situations had been imposed immediately.
Major powers condemn the attack
UN Secretary-General Ban Ki-moon described the attack as "one of the gravest incidents since the end of the Korean War" and called for restraint by both sides.
In the United States, the White House issued a statement "strongly condemning" the artillery attack and called on North Korea "to halt its belligerent action."
German minister said the incident endangered peace
German Foreign Minister Guido Westerwelle said he was "very worried about this newest development" and appealed for "moderation among the participants."
"This renewed provocation endangers peace in the region," Westerwelle said.
Japan, China and Russia also voiced deep concern over the incident.
Japanese Prime Minister Naoto Kan said he had ordered his cabinet ministers to prepare for any eventuality.
Russia warned against an escalation of tensions and called the attack "unacceptable." In Moscow, Foreign Minister Sergei Lavrov urged both sides to show restraint to prevent a wider conflict.
"There is a colossal danger, which must be avoided," Lavrov warned, adding that "those who started this bear a huge responsibility."
Yeonpyeong is in a sensitive border area of the Yellow Sea
South Korea's YTN television said air force jets were scrambled, after what appeared to be one of the most serious border incidents since the 1950-53 war. The two Koreas are still technically at war, as that conflict ended only in a truce.
Local islanders were evacuated to safe areas, and the military and police were checking the number of casualties, YTN reported. Residents were also said to be fleeing the island by fishing boat.
Unconfirmed eyewitness reports said that fires caused by the shelling were now burning out of control and spreading.
South Korea's Unification Ministry reportedly told YTN that it was considering evacuating its citizens in North Korea, who work at the Kaesong industrial park and Mount Kumgang resort.
Yeonpyeong island lies about three kilometers (1.8 miles) south of the sea border and 120 kilometers west of Seoul.
The Yellow Sea border was the scene of deadly naval clashes in 1999 and 2002, and the North's alleged involvement in the sinking of a South Korean ship there last November damaged already tense ties between the two neighbors.
Author: Gabriel Borrud, Gregg Benzow (AP, dpa, AFP, Reuters)
Editor: Nancy Isenson