Brawls erupt regularly between the two nuclear-armed giants across their disputed 3,500-kilometre (2,200-mile) frontier, but no one has been killed in decades.

But the Indian army said there were "casualties on both sides" in Monday's incident on the Himalayan frontier between China's Tibet and India's region Ladakh, although Beijing made no mention of any -- while laying the blame squarely on Delhi.

"A violent face-off took place yesterday (Monday) night with casualties on both sides. The loss of lives on the Indian side includes an officer and two soldiers," an Indian army spokesman said in a statement.

An Indian army officer in the region told AFP that there had been no shooting in the incident, on precipitous, rocky terrain in the strategically important Galwan Valley.

"It was violent hand-to-hand scuffles," the officer said on condition of anonymity. The officer killed was a colonel from

- 'Attacking Chinese personnel' -

Beijing confirmed a clash took place and accused Indian soldiers of crossing into Chinese territory and "attacking Chinese personnel".

Indian troops "crossed the border line twice... provoking and attacking Chinese personnel, resulting in serious physical confrontation between border forces on the two sides," China's foreign ministry spokesman Zhao Lijian said Tuesday.

"We again solemnly request that India follows the relevant attitude and restrains its frontline troops," he added.

China's defence ministry confirmed the incident had resulted in casualties but did not give the nationality of the victims or any other details.

India and China have long squabbled about their border but recent weeks have seen an escalation.

On May 9, several Indian and Chinese soldiers were injured in a clash involving fists and stone-throwing at Naku La in India's Sikkim state, which borders Bhutan, Nepal and China.

Alice Wells, the top US State Department official for South Asia, likely irked Beijing last month when she said that China was seeking to upset the regional balance and had to be "resisted".

But the Chinese foreign ministry said only last week that a "positive consensus" had been reached following "effective communication" through diplomatic and military channels.

India's foreign ministry too had sounded conciliatory, saying the two sides would "continue the military and diplomatic engagements to resolve the situation and to ensure peace and tranquillity in the border areas."

However, Indian sources and news reports suggested that Chinese troops remained in parts of the Galwan Valley and of the northern shore of the Pangong Tso lake that it occupied in recent weeks.

"We are at an extremely worrisome juncture in the relationship," former Indian ambassador to China and foreign secretary Nirupama Menon Rao told AFP.

- Prickly relations -

India and China have never even agreed on the length of their "Line of Actual Control" frontier, and each side uses different frontier proposals made by Britain to China in the 19th century to back their claims.

They fought a brief war in 1962 in which China took territory from India. Further deadly clashes followed in 1967, but the last shot fired in anger was in 1975.

In 2017 there was a 72-day showdown after Chinese forces moved into the disputed Doklam plateau on the China-India-Bhutan border.

After that India's Prime Minister Narendra Modi and Chinese leader Xi Jinping appeared to ease tensions at two summits.

"If not handled correctly this can really escalate into something much bigger than we had initially imagined," Harsh V Pant from the Observer Research Foundation think-tank told AFP, calling China's statement "worrying".

"China, with its better infrastructure, with its better military capabilities, perhaps thinks that this is the time to push India, to see how far India will go," Pant told AFP.

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