SEOUL, South Korea — South Korea on Sunday kicked off its biannual military exercises aimed at demonstrating control over a set of islets that are the source of a territorial dispute with Japan, a move that was likely to heighten tensions between Washington’s two key Asian allies.

Relations between Seoul and Tokyo are already in their worst state in years as the two nations have engaged in a tit-for-tat escalation of tensions over historical and trade disputes.

The two-day military exercise began three days after South Korea announced that it would terminate a military intelligence-sharing deal with Japan to retaliate against trade restrictions Tokyo had imposed earlier.

The drill involved an unannounced number of navy and coast guard ships, air force planes and army and marine troops and took place around Dokdo, a set of largely uninhabitable volcanic outcroppings off the east coast of South Korea. The country has administered Dokdo, keeping a contingent of armed coast guard officials there since the 1950s.