China’s defense ministry expressed its “dissatisfaction and opposition” Thursday over the crash of an Indian unmanned aerial vehicle inside Chinese territory, the latest in a series of border incidents between the regional rivals.

Chinese border troops identified the device and were dealing with the matter in a “professional and responsible manner,” the official Xinhua News Agency cited the deputy chief of the Chinese military’s Western Theater Command, Zhang Shuili, as saying.

“In regards to this matter, we express our strong dissatisfaction and opposition,” Zhang was cited as saying in the Xinhua article posted on the ministry’s website. “We will earnestly carry out our duty and resolutely defend our country’s sovereignty and security.”

A spokesman for the Chinese Foreign Ministry said the drone crashed in the Sikkim section of China’s border with India and that China has lodged a complaint with India over the issue.

“I want to point out that the Sikkim section of China-Indian border has been delineated. And Chinese side along the border line is Chinese territory,” spokesman Geng Shuang said. “The action of the Indian side violated China’s sovereignty and it’s not conducive to the peace and tranquility of the border area.”

No further information was given about the vehicle and when it crashed.

Col. Aman Anand, a spokesman of India’s Ministry of Defense, said the drone was on a regular training mission inside Indian territory when it “lost contact with the ground control due to some technical problem” and crossed the border in Sikkim.

Anand said Indian border security personnel immediately alerted their Chinese counterparts and said India was investigating the exact cause of the incident.

India operates a range of domestically developed UAVs and this summer agreed to buy top-of-the-line combat drones from Israel.

Much of the 3,500-kilometer (2,174-mile) border between China and India is contested. They fought a brief but bloody frontier war in 1962 and engaged in a 10-week standoff this summer high in the Himalayas over the Doklam plateau that is claimed both by China and India’s ally Bhutan. – AP