SINGAPORE - A landmark treaty between Singapore and Indonesia that demarcates maritime boundaries in the eastern part of the Strait of Singapore has come into force.

Foreign Minister Vivian Balakrishnan and his counterpart, Indonesian Foreign Minister Retno Marsudi, exchanged ratification instruments for the treaty in a ceremony at the Ministry of Foreign Affairs on Friday (Feb 10).

The treaty relating to the delimitation of the territorial seas of the two countries in the eastern part of the Strait of Singapore was signed by both countries in 2014. It covers a 9.5km stretch in the Singapore Strait between Changi and Batam.

The treaty was ratified by the Indonesian Parliament last December, and is the third of its kind between the two neighbours.

They first agreed on the maritime boundary along the central part of the Singapore Strait in 1973, and in 2009 signed another pact on the western section, between Indonesia's Pulau Nipa and Singapore's Sultan Shoal.

With the latest treaty in place, the three account for a continuous 67.3km-long sea border in the Singapore Strait.

One outstanding stretch remains to be demarcated between Pedra Branca and Bintan. But that will, however, have to wait for talks between Singapore and Malaysia on delimiting maritime boundaries around Pedra Branca, Middle Rocks and South Ledge.

Ms Retno is in Singapore on a visit that commemorates the 50th anniversary of diplomatic relations between the two countries. Earlier in the day, she spoke about Indonesia's foreign policy at a lecture organised by the S Rajaratnam School of International Studies.