The first attempts to define it precisely were made by the colonial powers of the Netherlands and Portugal with the Treaty of Lisbon in 1859, but it was not until the Permanent Court of Arbitration's award of 25 June 1914 that the final land border between them on the island of Timor was established.

[2] The Municipality of Oecusse forms an exclave of Timor-Leste in Indonesian West Timor (part of East Nusa Tenggara province).

The border between Indonesia and the main part of Timor-Leste starts in the north at the Savu Sea coast, and proceeds south and then east via the Talu river.

In 1749, an attempted reconquest by the Portuguese failed at the Battle of Penfui, whereupon most rulers in the west signed treaties with the Dutch East India Company.

Among them was a certain Jacinto Correa, King of Wewiku-Wehale and Grand Prince of Belu, who also signed the dubious Treaty of Paravicini on behalf of many territories in central Timor.

[5] In 1851, the Portuguese governor José Joaquim Lopes de Lima reached an agreement with the Dutch on the division of the colonies in the Lesser Sunda Islands.

[3][6] However, the exact course of the border was still unclear, and with Portuguese Noimuti and Dutch Maucatar, there was also one enclave each of the colonial power without access to the sea on the side of the competitor.

On 10 June 1893, An additional treaty, the Lisbon Convention, was then signed between the governments, with the intention of creating favourable conditions "for the development of civilisation and trade" and for the dissolution of the still existing enclaves (ratified 1894).

[7] In fact, on 30 August 1898, Germany and Britain agreed in the Angola Treaty on a joint bond for the heavily indebted Portugal, for which the Portuguese colonies were intended as a pledge.

In the meantime, however, Lakmaras had become a subject of the Empire of Lamaquitos in the Portuguese sphere of power and Maucatar would have to fall to Portugal as an enclave according to the previous agreements.

[12] Between 1 and 10 June 1909, a commission carried out a survey of the eastern boundary of Oecussi-Ambeno, but could not agree on the correct course and decided to transfer the open questions back to their governments.

[7] In the southern part, the commission investigated the demarcation along the course of the Nono Nisi (Nise) on 17 June 1909, then further along the course of the Noèl Bilomi, finally arriving at the point where the 1899 expedition had finished its work.

[7] However, the Dutch felt that there was no point in pursuing the survey of this river, as both Mount Kinapua and the border area that would be created under the Portuguese proposal were outside the territory contested in 1899.

A treaty was subsequently signed on 1 October 1904 (ratified 1908) which created the modern boundary, removing a number of enclaves whilst leaving the exclave of Oecusse as part of Portuguese Timor.

[3] The Joint Commission interrupted its work here and the question, meanwhile taken over by the diplomatic services, caused endless correspondence between the cabinets in The Hague and Lisbon.

Finally, in 1999, under pressure from the international community, a referendum was held in which the population had the choice between independence and belonging to Indonesia as an autonomous province.

The initial result was the 2005 Interim Agreement, which established a land boundary between Indonesia and Timor-Leste of 268.8 kilometers with 907 coordinate points.

The remaining 4% covering the Noel Besi-Citrana, Bidjael Sunan-Oben, and Dilumil-Memo areas had formerly not been agreed upon due to differences in border interpretation between the two countries.

Still in dispute was the affiliation of the small uninhabited island of Batek Island (Fatu Sinai), 37 hectares between the East Timorese village of Memo (Suco Tapo/Memo) and the Indonesian Dilumil (Lamaknen district, Belu Regency), where it was not possible to agree on the location of the river median of the Mathiaca (Malibaca) over a length of 2.2 km[18] and areas around the exclave of Oe-Cusse Ambeno (Área Cruz with 142.7 hectares in Passabe, Citrana triangle in Nitibe) as well as the exact modalities of a corridor from Oe-Cusse Ambeno to the main state territory.

On 23 July 2019, following a meeting between Timor-Leste's chief negotiator Xanana Gusmão and Wiranto, Indonesia's Coordinating Minister for Political, Legal and Security Affairs, it was stated that agreement had now been reached on the course of the country's border.

[22][23] On 21 January 2022, Gusmão reported to the Foreign Affairs, Defence and Security Commission of the National Parliament on the status of the negotiations.

[19] In 2017, Both countries had formed an organization, the Senior Official Consultation (or known as the SOC), in the task of discussing the technical details of resolving border issues.

[25] However, after the Timor-Leste delegation brought home the results of the agreement, there was rejection from parliament, especially regarding the land boundary of the Noel Besi-Citrana region, also known as Naktuka.

In 2023, a joint technical team led by chief negotiators Roberto Soares (Timor-Leste) and Abdul Kadir Jailani (Indonesia) finalised the demarcation of the land border.

The 76 poles with the new border demarcation in the Citrana Triangle cut off 270 hectares of agricultural land around the village of Naktuka, which had been cultivated by its inhabitants for decades, and allocated it to Indonesia.

The inhabitants of Naktuka explained that the territory had been part of Portugal in colonial times and had belonged to Timor Timur during the Indonesian occupation.

[27][28][29] Timor-Leste's President José Ramos-Horta stated that there were ‘still reasons’ to continue the discussion on the land border with Indonesia and expressed ‘optimism with regard to a joint solution’.

[32] In a statement published on Facebook on January 31 by his party, January, his party, the CNRT, stated that while the arbitration award between the Netherlands and Portugal did indeed award Naktuka entirely to Portugal, the historical border between the realms of Amfo'an (on the Dutch side) and Ambeno (on the Portuguese side) was the Noel Besi River, so Naktuka must belong entirely to Indonesia.

Gusmão explained that in 2014, during his last term as prime minister, he had promised Indonesia that Indonesian farmers who cultivate land in Naktuka would not be evicted.

The Prime Minister stated that the border agreement should now be signed in September during the visit of Indonesian President Joko Widodo to Timor-Leste.