POHANG, South Korea (AFP) - Thousands of US and South Korean troops, backed by helicopters and jet fighters, staged a massive, amphibious landing drill on Monday - the centrepiece of an annual military exercise condemned by North Korea.

A total of 7,600 soldiers, including 3,500 marines, along with 80 aircraft, 30 ships, and scores of armoured vehicles and tanks, took part in the drill to secure a bridgehead along the coast of Pohang, some 360km south of Seoul.

Supervised by US and South Korean military commanders, the landing exercise was the highlight of the eight-week Foal Eagle drill which is scheduled to end on April 24.

The annual drills always trigger a surge in military tensions between the two Koreas, which remain technically at war because the 1950-53 Korean conflict ended with a ceasefire rather than a peace treaty.

The United States and South Korea insist the joint exercises are defensive in nature, but North Korea denounces them as provocative rehearsals for invasion.