"Eight MK-82 general-purpose bombs were abnormally released from an Air Force KF-16 aircraft, landing outside the designated firing range," the Air Force said.

The incident occurred around 10:00 am (0100 GMT) in Pocheon, around 25 kilometres (16 miles) south of the heavily fortified border with the nuclear-armed North.

"We deeply regret the unintended release of the bombs, which resulted in civilian casualties, and wish those injured a swift recovery," the Air Force said in a statement.

It said it had established an accident response committee to investigate the incident, and said it would "take all necessary measures, including compensation for damages."

The Air Force said the military jet had been "participating in a joint live-fire exercise involving both the Air Force and Army."

South Korea was holding combined live-fire drills with the United States Thursday in Pocheon, the Yonhap news agency reported.

South Korea's National Fire Agency said that the bombs were "presumed to have fallen on a village during a South Korea-US joint exercise."

This resulted in "casualties and property damage, with many displaced residents," it said, adding that four people had been seriously injured and three suffered minor injuries.

One church building and sections of two houses were damaged, according to the statement.

Joint South Korea-US "Freedom Shield" military exercises, one of the security allies' largest annual joint exercises, are set to begin later this month.

The two Koreas remain technically at war since the 1950-1953 conflict ended in an armistice, not a peace treaty.

The United States stations tens of thousands of soldiers in the South, in part to protect Seoul against Pyongyang.