India warned China on Friday that construction of a road near their common border would have serious security implications, as China's Foreign Ministry denied its troops had violated the territory of India's ally, Bhutan.
The standoff on a plateau next to the mountainous Indian state of Sikkim, which borders China, has ratcheted up tension between the two neighboring giants, who share a 3,500 km (2175 miles) frontier, parts of which are disputed.
According to the Chinese interpretation of events, Indian guards crossed into China's Donglang region early in June and obstructed work on a road on a plateau.
Troops from the two sides then confronted each other close to a strategic valley controlled by China that separates India from Bhutan and gives China access to the so-called Chicken's Neck, a thin strip of land that connects India to its remote northeastern regions.
Bhutan said on Thursday that the road was being built inside its territory.
Indian media have reported that the dispute began when China removed an old Indian bunker.
"India is deeply concerned at the recent Chinese actions and has conveyed to the Chinese Government that such construction would represent a significant change of status quo with serious security implications for India," India's ministry of external affairs said in a statement.
"It is essential that all parties concerned display utmost restraint and abide by their respective bilateral understandings not to change the status quo unilaterally," the ministry said.
Chinese Foreign Ministry spokesman Lu Kang said the road work was going on in an area that was on the Chinese not Bhutanese side.
China and Bhutan have yet to reach a final agreement on demarking their border.
Indian army chief visits border
India's army chief visited Sikkim on Thursday, where tensions have flared after Beijing accused New Delhi of sending troops into its territory and obstructing the construction of a road.
Small incursions and troop stand-offs are common along other parts of China and India's contested 3,500-kilometer frontier, but a flare-up near strategically positioned Sikkim is rare.
General Bipin Rawat arrived in Gangtok, the capital of the tiny Himalayan state, before heading off to visit troop formations. A spokesman for the Indian army said the one-day trip was "routine" and planned before the recent tensions.
Reports of the incursion and a confrontation between troops emerged as Prime Minister Narendra Modi arrived in Washington to meet US President Donald Trump on Monday, the latest in a line of stand-offs reported during diplomatic initiatives.
India has deepened its military ties with the United States in recent years, worrying China, which is also unhappy with India's refusal to participate in Beijing's multi-billion-dollar Belt and Road infrastructure initiative. India is concerned the project could cement China's dominance over Asia.
China says that unlike other parts of their shared border, the delineation of the frontier with Sikkim is settled, and it has the right to develop the area.
"Donglang Region is part of China's territory," Lu said on Thursday. "China's road-building activities in Donglang on its own territory are totally reasonable and understandable."
The Nathu La Pass, which lies on the frontier between Sikkim and Tibet, was the site of a fierce border clash between Chinese and Indian troops in 1967.