India says at least 20 of its soldiers were killed after hand-to-hand fighting with Chinese troops at a disputed border site on Monday night, in the deadliest clash between the two Asian giants in decades.

China said its troops were engaged in a “violent physical confrontation” with Indian soldiers, but has given no details of those killed or wounded.

Both Indian and Chinese officials accuse each other of crossing the Line of Actual Control (LAC), the de facto border between the nuclear-armed Asian giants. The LAC is largely based on the ceasefire line after the war in 1962, but both sides disagree on where it lies.

The latest clashes took place at a disputed border site in the Galwan area of Ladakh, in the western Himalayas, an area at an altitude of around 14,000 feet where temperatures often fall below freezing.

The disputed site lies amid remote jagged mountains and fast-flowing rivers on the northern tip of India, abutting the Aksai Chin Plateau, which is claimed by India but administered by China.

Both countries claim vast swaths of each other’s territory along the Himalayan border, with some disagreements rooted in demarcations by British colonial administrators of India.

India and China fought a brief but bloody border war in 1962 and distrust has occasionally led to flare-ups ever since. Infrastructure building near or within disputed territories is often blamed for increases in tensions.

The last major dispute took place in 2017 on the remote Doklam plateau near the borders of India, Bhutan, and China, at the eastern end of the 4,056-km (2,520-mile) long border. After a tense standoff, both sides agreed to an “expeditious disengagement” of troops.