Why are Chinese and Indian troops fighting in a remote Himalayan valley?

CHINA - BEIJING. The Indian army 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, the deadliest clash in decades.

China has not given any details of casualties.

Where was the latest fighting?

The clashes took place in the Galwan region of Ladakh, in the western Himalayas, where Indian and Chinese forces have been facing off since early May.

The disputed site lies amid remote, jagged mountains and fast flowing rivers on the northern tip of India, abutting the Aksai Chin plateau, a Chinese administered area claimed by India.

The area lies at an altitude of about 14,000 feet (4,250 metres) and temperatures often fall below zero degrees Celsius.

A 1993 agreement between the two countries stipulates that neither side shall use force at the Line of Actual Control (LAC), the de facto border. But violent, high-altitude disputes have erupted several times without any shots being fired.

Why did clashes erupt now?

Both countries claim vast swathes of each other's territory along their 4,056 km (2,520 mile) Himalayan border. Some disagreements are rooted in demarcations made by India's former British colonial administrators.

Military experts say one reason for the current face-off is that India has been building roads and airfields to improve transport links and narrow the gap with China's superior infrastructure on its side of the LAC.