North Korea fired over its heavily fortified southern border Friday, and South Korea retaliated in a rare instance of their cold war turning hot less than two weeks before President Barack Obama and other world leaders are due in Seoul for a global economic summit.
It was unclear late Friday whether North Korea's firing of 14.5-mm rounds at a South Korean guard post in the Demilitarized Zone was an accident or an intentional provocation, an official with the Joint Chief of Staff in Seoul said.
However, the shooting -- the first at the border since 2007 -- came just hours after North Korea threatened to retaliate for South Korea's refusal last week to hold military talks with its wartime rival.
South Korean soldiers immediately returned fire, but sustained no injuries, according to the Joint Chiefs official, who asked not to be identified because he was not authorized to speak to the media. There was no word from the North on either the incident or injuries.
The exchange lasted just a few minutes but highlighted the security challenges South Korea faces as it prepares to host next month's Group of 20 summit in Seoul, just 30 miles (50 kilometers) from the border.
The firing underscores the unusual -- almost surreal -- world South Korea inhabits: Though a major global economy and a political leader in Asia with one of the highest standards of living in the world, the South is still technically at war with the North because their conflict ended in a truce, not a peace treaty. Tens of thousands of troops stand guard on both sides of the border dividing the Koreas.
Communist North Korea has a track record of provocations against South Korea at times of internal change, external pressure or when world attention is focused on Seoul.
"The North wants to show the world that military tension grips the Korean peninsula," said Kim Yong-hyun, an expert on North Korean affairs at Seoul's Dongguk University.
In 1987, a year before Seoul hosted the Summer Olympics, North Korean agents planted a bomb on a South Korean plane, killing all 115 people on board. In 2002, when South Korea was jointly hosting soccer's World Cup along with Japan, a North Korean naval boat sank a South Korean patrol vessel near their disputed western sea border.
Analyst Lee Sang-hyun of the Sejong Institute, a private security think tank outside Seoul, agreed that the North was probably hoping to humiliate South Korean President Lee Myung-bak on the eve of the G-20. But he remained cautious about whether the firing was an isolated incident or could signal further provocations against the South.
Tensions have been particularly high since the March sinking of a South Korean warship in the waters off the peninsula's west coast. Forty-six sailors died in the sinking, which an international panel blamed on a North Korean torpedo; Pyongyang, however, denies involvement.
But more recently, the North has made a series of conciliatory gestures, and relations seemed to be beginning to thaw.
North Korea recently proposed talks to discuss anti-North Korean leafletting by South Korean activists and other propaganda activities, Pyongyang's official Korean Central News Agency reported Friday.
When Seoul rejected the proposal, the army threatened a "merciless physical retaliation" Friday for the snub, KCNA said. It promised South Korea would realize "what catastrophic impact their rejection of dialogue will have on the North-South relations."
In Seoul, a Defense Ministry official said the military talks proposed last week by the North did not take place because the two Koreas remain at odds over the sinking of the Cheonan. He spoke on condition of anonymity, citing internal policy.
Pyongyang had warned during military talks in late September that it could fire artillery at sites in the South where civilian activists set off huge helium balloons filled with leaflets condemning North Korean leader Kim Jong Il, pushing them across the border.
The North views the leaflets -- which activists hope will persuade North Koreans to rise up against Kim -- as part of psychological warfare aimed at toppling its regime. Seoul says it cannot ban its citizens from expressing their opinion.
Despite the spike in tensions Friday, the reunions of hundreds of families separated by the Korean War will go ahead Saturday in the North Korean resort of Diamond Mountain as scheduled, South Korean Unification Ministry spokesman Chun Hae-sung said.
Shooting incidents at the border are infrequent; the last border shooting was in 2007, when South Korea said North Korean soldiers opened fire and the South shot back, according to the JSC.
However, North Korean troops fired some 30 artillery rounds near the western maritime border in January, prompting the South to fire 100 warning shots in response.