SEOUL, Oct 29 (Reuters) - North and South Korea exchanged gunfire across their heavily armed land border on Friday, the South's military said, despite an apparent thaw in tensions on the divided peninsula in the past few months. The rare exchange of fire took place a fortnight before the leaders of the world's 20 top economies meet for a G20 summit in the South Korean capital Seoul, about 100 km (60 miles) south of the demilitarised zone.
The South's defence ministry said in a statement none of its troops were hurt, and there had been "no more unusual activity by the North". A South Korean military official said the army had put on heightened alert.
It was not immediately clear what was behind the skirmish, but in the past the North has carried out similar provocations around the time the South has hosted prominent international events.
YTN television said, however, it was unlikely that the North had deliberately fired across toward the South only hours before families separated by the 1950-53 Korean War were due to be reunited for the first time
The North Korean frontline guard post fired two shots towards a South Korean guardpost across the DMZ and the South returned fire with three shots, a joint chiefs of staff official said.
The South Korea military official said he had not received any communication from the North. A United Nations team will be sent to the area on Saturday, he added.
The North Korean shots were fired at a frontline unit in Cheorwon in the eastern province of Gangwon.
The last time the two Koreas were exchanged fire was in January, the they fired artillery round at disputed sea border.
Relations between the two Koreas, still technically at war after signing only a truce to halt hostilities in the 1950-53 Korean War, sank to the lowest level in years in March with the torpedoing of the South's warship, killing 46 sailors
South Korea and the United States said the North was responsible for the sinking, but Pyongyang denied any role.
In the past few months, tensions have eased on the peninsula with the South sending aid to its impoverished neighbour, and on the weekend the two sides will resume the reunions.
But the border skirmish and news that North-South military talks had broken down showed that the two sides were still far apart, and underlined there was little chance of a resumption any time soon of stalled talks on the North's nuclear arms programme.
South Korea rejected the North's proposal for more military talks and said it wouldn't return to the negotiating table until its neighbour admited responsibility for the sinking of the warship.
"When looking back on the history of the North-South relations, it is very hard to find a precedent in which one party rejected the talks proposed by the other party even when the bilateral relations reached the lowest ebb," the North's KCNA state news agency reported.
"This was because the rejection of dialogue precisely meant confrontation and war."
This weekend's resumption of family reunions, which were last held over a year ago, was the most tangible sign yet of a thaw in tensions. Earlier this week, South Korean government sent its first delivery of aid to the North in more than two years.