The incident follows rising tensions and is the first deadly clash in the border area in at least 45 years.
At least three Indian soldiers were killed as border tensions between China and India flared on Monday.
A long-running conflict between India and China in the Himalayas erupted into gunfire on Monday, killing at least three members of India’s military.
The Indian army said in a statement on Tuesday that one of its officers and two of its soldiers were killed during what is called a “violent face-off” in the Galwan Valley in the region of Ladakh.
According to the AFP news agency, India said there were also Chinese casualties, but did not give a figure.
The area is a disputed land border between the two countries, CNN reported. India and China went to war over the border in the 1960s and never formally agreed on boundaries since, resulting in an uneasy conflict lasting decades.
Zhao Lijian, China’s Foreign Ministry spokesman, said on Tuesday that Indian personnel crossed the border and attacked Chinese troops. Zhao did not say if there had been any injuries or fatalities.
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He said: “Indian troops seriously violated our consensus and twice crossed the borderline for illegal activities and provoked and attacked Chinese personnel which leads to serious physical conflict between the two sides,” according to CNN.
Both countries have been in a standoff in the region for weeks, Reuters reported the latest in a decades-long dispute over the border and disputed territory as both countries claim part of the region as their own.
India’s army said the latest incident took place during a “de-escalation process.”
CNN reported last week that Chinese state media was showing footage of planes and trucks filled with troops operating in the region.
China’s state-run Global Times reported on an operation involving “thousands of paratroopers plus armored vehicles” in early June, saying experts said it showed “China’s capability of quickly reinforcing border defenses when necessary.”
Zhao said in his Tuesday briefing that China wanted peace in the region and that the countries are in talks.
“China has lodged strong protest and representation with the India side, and we once again we solemnly ask the India side to follow our consensus and strictly regulate its front line troops and do not cross the line and do not stir up troubles or take unilateral moves that may complicate matters,” he said.
“We both agreed to resolve this issue through dialogue and consolation and make efforts for easing the situation and upholding peace and tranquility in the border area.”