Nepal has lodged a formal diplomatic protest with India over the resumption of a religious pilgrimage through the disputed Lipulekh Pass, reviving a long-running border dispute between the two neighbours.

Kathmandu's Ministry of Foreign Affairs lodged the protest on Sunday, criticising New Delhi for resuming the Kailash Manasarovar pilgrimage through the Himalayan pass, which sits at the junction where Nepal meets India and Tibet. Nepal claims the pass on the basis of the 1816 Treaty of Sugauli, signed with India's British colonial rulers to define its western border.

In its complaint, the ministry stressed that the territories of Limpiyadhura, Lipulekh and Kalapani are part of Nepal, "a position on which the government remains clear and firm". Foreign Minister Shishir Khanal said the protest followed consultations with political parties and that Nepal's stance has been formally communicated.

The dispute flared again after India announced on Thursday that it had agreed with China that the pilgrimage via Lipulekh would resume. The route was suspended in 2020 because of the COVID-19 pandemic. Under the plan, 500 Hindu pilgrims will travel through the northern Indian state of Uttarakhand to cross into China at the Lipulekh Pass, while others will use a separate route through the northeastern state of Sikkim.

India's Ministry of External Affairs rejected Nepal's objection, asserting that Lipulekh has been used by Hindus, Buddhists, Jains and Bon followers for the pilgrimage to Mount Kailash and Lake Manasarovar in Tibet since 1954. "This is not a new development," a spokesman said. "India has consistently maintained that such claims are neither justified nor based on historical facts and evidence. Such unilateral artificial enlargement of territorial claims is untenable."

Kathmandu has long urged India not to undertake road construction, border trade or pilgrimage activity in the area without its consent, calling the matter sensitive. This is Nepal's second protest over the pass since August last year, when India and China opened a trade route through the same disputed mountainous region.

Nepal says it remains committed to resolving the boundary issue through "historical facts, evidence and diplomatic dialogue". The Kailash Manasarovar pilgrimage is one of Hinduism's most revered journeys, and the Lipulekh route is one of two main corridors used for it, organised in coordination with China.

The row is the latest flare-up in a dispute that has strained relations between the neighbours for years. Nepal published a new political map in 2020 including the disputed areas, and India has repeatedly rejected the claim, insisting the territory is part of the Indian state of Uttarakhand and has been under its administration for decades. No talks have yet been announced to settle the latest protest, and there is no indication so far that the planned pilgrimage route will change.