China admonished the United States on Monday for sending its ambassador in India to Arunachal Pradesh, warning that a third party's meddling would only complicate the dispute between Beijing and New Delhi.
India firmly rejects China's claim to more than 90,000 sq km (35,000 sq miles) of territory in the eastern Himalayas. Much of that forms Arunachal Pradesh, which China contentiously calls South Tibet.
US Ambassador to India Richard Verma posted photos on his Twitter account on October 21 of his recent trip to Arunachal Pradesh, thanking officials for their "warm hospitality" and calling the region a "magical place".
Chinese Foreign Ministry spokesman Lu Kang said China was "firmly opposed" to the US diplomat's actions, which he said would "damage the hard-earned peace and tranquillity of the China-India border region".
Stunning mountains & wonderful people. Terrific visit to #ArunachalPradesh for the #TawangFestival. Thank you Tawang for the hospitality. pic.twitter.com/WdpVZg0J3X
— Rich Verma (@USAmbIndia) October 21, 2016
"We urge the United States to stop getting involved in the China-India territorial dispute and do more to benefit this region's peace and tranquillity," he said, adding that China and India were handling the matter appropriately through talks.
A spokesman for India's Ministry of External Affairs was not immediately available for comment according to news agency Reuters.
In August, China was angered by India's plans to place advanced cruise missiles in Arunachal Pradesh. The army, dismissing those complaints, said it would take all decisions based on India's security interests.
India says China occupies 38,000 square km (14,600 sq miles) of its territory on the Aksai Chin plateau in the west, and is suspicious of China's escalating support for Pakistan at a time of the worst tension in over a decade between Delhi and Islamabad.