Communist North Korea invaded the US-backed South on June 25, 1950, triggering a three-year war that killed hundreds of thousands of soldiers.

Some 147 sets of remains were flown on a South Korean military aircraft from Hawaii, where they were previously sent by the North following their discovery over the past three decades.

The plane was escorted into the country Wednesday by six fighter jets in honour of the fallen.

Pictures showed small white coffins individually wrapped in South Korean flags occupying seats on the plane.

Some of the remains were recovered during excavations by the North between 1990 and 1994, while others were sent by Pyongyang following a Singapore summit between leader Kim Jong Un and US President Donald Trump in 2018, according to Seoul's defence ministry.

"After a long detour of 70 years, they are finally home," it said.

The remains were classified as South Koreans through joint US-South Korea forensic reviews in Hawaii, but only seven soldiers have been identified and authorities will carry out further checks to try to name the others.

The known seven will be awarded service medals at a ceremony Thursday, along with six sets of remains from identified Americans.

Wednesday's arrival at a Seoul airbase is the fourth batch of repatriations and brings the total to 239.

Millions died in the three-year conflict, with Seoul's defence ministry putting military fatalities at 520,000 North Koreans, 137,000 Southern troops and 37,000 Americans.

Washington still stations 28,500 troops in the South, while the North -- which has the world's largest standing army -- has spent decades developing nuclear weapons and long-range missiles, saying it needs them to deter a US invasion.