South Korean President Moon Jae-in sent a condolence letter to his Indonesian counterpart, Joko Widodo, over the deadly sinking of the country's naval submarine, Cheong Wa Dae said Tuesday.

Moon expressed regret about the deaths of 53 crew members and delivered a message of condolences and sympathy to the Indonesian people, according to presidential spokesperson Park Kyung-mee.

He hoped that the Indonesian people will overcome grief from the tragic accident at an early date, she added.

Indonesia is a key partner of the Moon administration's New Southern Policy aimed at improving strategic ties with countries in South Asia.

Seoul and Jakarta have been developing "special friendly cooperative relations" in the economy, defense and arms production, Park pointed out.

The submarine went missing last week while taking part in a torpedo drill off the coast of Bali. It was found split into three pieces on the sea bed, with all of the 53 crew confirmed dead. (Yonhap)