Tensions between India and China on Monday mounted again, after they accused each other of trying to seize territory across their disputed Himalayan border.

Accusations flew between the world's two most populous nations just two months after high-altitude hand-to-hand combat between their troops that left at least 20 Indian soldiers dead.

India accused China of seeking to cross their unofficial border in the Ladakh region late Saturday, while Beijing countered that Indian troops tried their own mission on Monday. 

Both sides said they were determined to defend their territory. 

Hostility between the nuclear-armed neighbours is now at some of the highest levels since they fought a border war in 1962.

The two countries have sent tens of thousands of troops, backed by tanks and fighter jets, to the region since the brutal June 15 battle fought with wooden clubs and fists in which China suffered an undisclosed number of casualties. 

A military accord between the two prohibits the use of firearms on the border.

Diplomatic and military talks since have made little apparent progress and their rancour became apparent in descriptions of the latest showdown.

India's defence ministry said on Monday that Chinese troops "carried out provocative military movements to change the status quo" on Saturday.

- 'Large number of Chinese forces' -

China's People's Liberation Army regional command said in a statement that India was "seriously violating China's territorial sovereignty" with its operation staged Monday and demanded that Indian troops withdraw.

Indian officials would not comment on the Chinese claims.

Indian media reports, quoting military sources, said PLA forces tried to take hilltops traditionally claimed by India around Pangong Tso, a lake at 4,200 metres (13,500 feet) altitude.

"Indian troops pre-empted this PLA activity on the southern bank of Pangong Tso lake, undertook measures to strengthen our positions and thwart Chinese intentions to unilaterally change facts on ground," said India's defence ministry.

The Business Standard newspaper said that on Monday a special Indian force tried to take heights that China considers its own.

The PLA statement said Indian forces engaged in "open provocation and caused the border situation to become tense." It said China was taking "necessary counter-measures".

China's foreign ministry said earlier its troops have "always strictly respected" the border that has never been officially delineated.

Residents of Leh, the main city in Ladakh, said the main road to the conflict zone was again closed amid a new surge of military convoys to the border.

The incursions made national headlines and rattled India's stock market in Mumbai, with the main Sensex index losing more than two percent following reports of the new showdown with the giant neighbour.  

Amid calls for boycotts of Chinese goods, India has stepped up economic pressure on China since the June battle and repeatedly warned that relations would suffer unless its troops pull back. 

India has banned at least 49 Chinese owned-apps, including the TikTok video platform, frozen Chinese firms out of contracts, including for India's 5G mobile phone upgrade and held up Chinese goods at customs posts.

China has complained about the action and warned that Indian consumers will suffer.

"We have very large number of Chinese forces (at the border) and frankly we are at a loss to know why," Foreign Minister S. Jaishankar said in an interview with the Hindustan Times released Sunday.