A stray military drone has added to the strains in India-China relations ahead of External Affairs Minister Sushma Swaraj's meeting with Chinese Foreign Minister Wang Yi in New Delhi next week.

New Delhi on Thursday stated that an Unmanned Aerial Vehicle (UAV aka drone) of the Indian Army strayed across the Line of Actual Control (LAC) in Sikkim Sector after losing contact with the ground control due to "some technical problem". The Ministry of Defence issued the statement in New Delhi after China formally lodged a protest with India over the incident.

The LAC serves as the de facto border between India and China in the absence of settled boundary.

China's state-run news agency Xinhua on Thursday reported that the military of the communist country had "voiced strong dissatisfaction and opposition to the Indian UAV's intrusion" into the airspace of China.

The Xinhua quoted Zhang Shuili, deputy head of the combat bureau of the Western Theater Command of Chinese People's Liberation Army, as saying that India's move had "infringed upon the territorial sovereignty" of China.

"We are strongly dissatisfied with and opposed to this," said Zhang. "We will fulfil our mission and responsibility and defend China's national sovereignty and security resolutely," he said.

The Indian Army said that India's border security personnel had immediately alerted their Chinese counterparts to locate the UAV. "In response, the Chinese side reverted with the location details of the UAV. The exact cause of the incident is under investigation. The matter is being dealt with in accordance with established protocols through institutional mechanisms to deal with situations along the India-China border areas," said Indian Army spokesperson.

Neither New Delhi nor Beijing specified where and when the UAV had strayed across the LAC and flew into the territory claimed by China.

Doklam face-off

The Sikkim Sector of the disputed Sino-India boundary came under international focus earlier this year, as the Indian Army and the Chinese People's Liberation Army had a 72-day face-off at Doklam Plateau in western Bhutan. It ended on August 28 last, but tension continued to prevail, not only in Sikkim Sector, but also the entire stretch of the disputed boundary.

Beijing also conveyed its concerns to New Delhi through diplomatic channels. "China asks India to immediately stop its activities of using unmanned aircraft near the border, and to work alongside China to maintain the border area's peace and tranquillity," Geng Shuang, a spokesperson of the Ministry of Foreign Affairs of Chinese Government, told journalists in Beijing.

The incident took place at a time when India and China lined up back-to-back engagements to mend bilateral relations, which hit a new low during the military face-off at Doklam Plateau.

The NITI Aayog vice-chairman Rajiv Kumar had a meeting with Li Wei, president of Development Research Council of China, in Beijing on Tuesday. External Affairs Minister Sushma Swaraj is set to hold a bilateral meeting with Chinese Foreign Minister Wang Yi on the sideline of the Russia-India-China trilateral talks in New Delhi early next week. The meeting between Swaraj and Wang is likely to be followed by the 20th round of boundary negotiation by the Special Representatives of India and China – Prime Minister Narendra Modi's National Security Advisor Ajit Doval and Chinese State Councillor Yang Jiechi.