South Korea on Monday began two days of war games to practise defending the disputed Dokdo islands off its east coast against an unlikely attack by Japan, angering Tokyo as it discusses ending joint drills with the US in a bid for peace with North Korea.
The drills come just days after US President Donald Trump announced the suspension of long-running US joint exercises with South Korea – aimed at deterring North Korea – calling them expensive and "provocative".
The two-day exercise – tiny compared with the suspended US-South Korea war games – will involve six warships and seven aircraft, and had begun, Seoul's defence ministry said. The drills are expected to last two days.
A unit of marines will land on the largely barren rocky islets, known as Takeshima in Japan and inhabited by about 40 people – mostly police officers.
"The Dokdo defence drill is a routine training conducted to prevent an invasion from external forces," said Choi Hyun-soo, a spokeswoman at Seoul's defence ministry.
Tokyo reacted angrily to the drills, with the foreign ministry saying it had "strongly protested" via the usual diplomatic channels.
On Sunday, it called on South Korea to stop the exercises.
"From Japan's position on territorial right of Takeshima, we can't accept this case at all and it is extremely regrettable," a ministry statement said.
It said the exercises were "absolutely unacceptable" and strongly demanded their suspension.
While an attack from Japan is deemed highly unlikely, South Korea first staged the drills in 1986 and has conducted them twice a year since 2003.
Seoul has controlled the islets in the Sea of Japan (East Sea) since the end in 1945 of Japan's 35-year colonial rule over the Korean peninsula.
Tokyo also claims the islands, and accuses Seoul of occupying them illegally. It has claimed ownership of the islands since the 17th century. The South says its ownership dates back to the sixth century.
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 severely strained by historical and territorial issues.
The two neighbours also have a long-running feud over Japan's use of Korean women as wartime sex slaves, despite an agreement in 2015 to settle the issue.