Seoul has controlled the islets in the Sea of Japan (East Sea) since the end of Japanese colonial rule on the Korean peninsula.

Tokyo also claims the islands, known as Takeshima in Japan, accusing Seoul of occupying them illegally.

The drills come just days after US President Donald Trump announced the suspension of long-running joint exercises with South Korea -- aimed at defending against North Korean aggression -- calling them "expensive" and "provocative".

While an attack from Japan is deemed unlikely, South Korea first staged the drills in 1986 and has conducted them twice a year since 2003.

"The Dokdo defence drill is a routine training conducted to prevent an invasion from external forces," Choi Hyun-soo, a spokeswoman at Seoul's defence ministry, said.

The two-day training -- tiny compared with the suspended US-South Korea war games -- will involve six warships and seven aircraft while a unit of marines will land on the largely bare rocky islets, inhabited by around 40 people -- mostly police officers.

South Korea and Japan are both market economies, democracies and US allies, and both are threatened by nuclear-armed North Korea, but their relationship is heavily strained by historical and territorial issues.

The two neighbours are also mired in a long-running feud over Japan's wartime sexual slavery of Korean women despite an agreement to settle the issue in 2015.