Nepal says it cannot locate the original documents of the treaty establishing its boundary with India, complicating the border dispute between the neighbouring South Asian nations.

Foreign minister Shisir Khanal told the parliament that Nepal did not “have clear information on whether we possess the official treaty documents”.

The Sugauli Treaty was signed in 1816 after the British East India Company defeated the Kingdom of Nepal in the Anglo-Nepalese War. The treaty significantly reduced Nepal’s territory by compelling the Himalayan kingdom to give up swathes of land in the west and the east that would eventually become part of independent India.

“There are records showing that some documents related to certain treaties are kept at the National Archives. But we don’t have clear information as to whether those are the actual official treaties," Mr Khanal said.

The search for the treaty papers began in 2016 after Nepal and India launched talks to review or replace the 1950 Treaty of Peace and Friendship.

The Nepali side wanted to examine the original copy of the treaty, but could not locate it. So, the government gave the committee reviewing the treaty a second copy instead.

On 22 July, the National Assembly's Delegated Legislation and Governance Committee said it had searched archives, libraries, museums, and relevant government departments but couldn’t find the original copy of either the Sugauli Treaty or the 1950 Treaty.

Relations between India and Nepal have grown tense lately as the new Balendra Shah government in Kathmandu has ramped up rhetoric against Delhi over the border dispute.

The long-running territorial dispute is centred on Kalapani, Limpiyadhura and Lipulekh areas in the far west of Nepal. Kathmandu says these are Nepali territories under the 1816 treaty, which sets the Kali river, also known as Mahakali, as the boundary.

The core disagreement is over where the river begins, with the rivals relying on different historical maps and interpretations.

Tensions flared after Delhi and Beijing agreed to reopen the disputed Lipulekh trade route to resume the traditional Kailash-Mansarovar pilgrimage.

Mr Shah fanned the flames by claiming that Nepal had encroached on Indian territory, a departure from the usual stance of accusing its bigger neighbour of occupying the Himalayan nation’s land. “You will be surprised to know a fact that I have learned recently, only after becoming prime minister. Not only has India encroached Nepali territory, but Nepal has also encroached Indian territory in many places,” the new leader said in his first formal address to the parliament.

The comments drew anger from Nepali lawmakers, who demanded the prime minister take back his words.

The foreign minister said Nepal would review all its treaties and agreements in line with its national interests. He said Kathmandu had 655 treaties and agreements, including 412 bilateral agreements with neighbouring countries.