SEOUL: North and South Korea on Thursday separately marked the 70th anniversary of the start of the Korean War, a conflict that killed millions of people and has technically yet to end.

Communist North Korea invaded the US-backed South on June 25, 1950, as it sought to reunify by force the peninsula Moscow and Washington had divided at the end of the Second World War.

The fighting ended with an armistice that was never replaced by a peace treaty, leaving the peninsula and millions of families split by the Demilitarized Zone.

In the South, the remains of nearly 150 soldiers repatriated from Hawaii after being excavated in the North were to be formally received at a government ceremony on Thursday evening, themed "Salute to the Heroes".

It was scheduled to include video messages from the leaders of the 22 foreign nations that made up the UN coalition defending the South, starting with President Donald Trump of the United States, which led the UN alliance.

Earlier, Seoul and Washington's defence ministers reaffirmed their commitment to defending "the hard-fought peace".

"On this day in 1950, the US-ROK military alliance was born of necessity and forged in blood," said US Secretary of Defence Mark Esper and his South Korean counterpart Jeong Kyeong-doo.

Up to three million Koreans died in the conflict, the vast majority of them civilians.

Nearly 37,000 Americans were among the more than 40,000 UN soldiers killed, and Western estimates say China, which backed the North, saw 400,000 fatalities, while Chinese sources put it at about 180,000.

The North has a different history of the period, which it knows as the Victorious Fatherland Liberation War, and insists that it was assaulted first, before it counter-attacked.