Chinese soldiers are making incursions into new stretches in the northeast to assert their claim over several border areas. At least 265 such incidents have been reported since January 2005, a top paramilitary official said.
"They are exploring new stretches in the northeast… Their penetration is five to six kilometres," Vineet Kumar Joshi, director-general of the Indo-Tibetan Border Police, told the Hindustan Times.
"They leave the vehicles at the border and walk in small groups, stay there for some hours and leave tell-tale signs like cigarette packets and packed food tins," Joshi added.
The Chinese Embassy in New Delhi rejected the allegation. "Currently, Indo-China border area enjoys a peaceful and tranquil situation. The story you have heard is totally groundless,'' it said in a written response to questions from the Hindustan Times.
At the heart of the rival assertions is the four-decade-old border dispute. Since the India-China war in 1962, what Indian maps show as national territory is not entirely recognised as such by the Chinese government.
The border issue is expected to be discussed in November when Chinese President Hu Jintao may visit India.
Apart from the parts of Jammu and Kashmir that are under Chinese control, there are vast disputed areas in the north and northeast - mainly in Arunachal Pradesh - where the impossible terrain is sparsely patrolled by India, with just a few border posts.
The incursions allegedly take place at Track Junction in the Karakoram region, and in Ladakh, including in the Pangong Lake - a 100-kilometre, narrow brackish water expanse.
Joshi said 33 kilometres of the lake lie in Indian territory, and the rest are controlled by the Chinese, who he said make regular intrusions on motorboats.
"They continue the incursions to make a point… to establish that this is not yet a settled issue,'' Joshi said.
India and China are currently holding talks to resolve their border dispute. Eight rounds have been held so far, the last one in June in China.
"The boundary question between China and India is a problem left from history," the Chinese statement said. "Before the final settlement, both sides should work together to keep peace and tranquillity of the border areas."
The ITBP is also facing shortage of resources - its 35,000-odd soldiers patrol some 3,500 kilometres of the border, at oxygen-sapped heights of up to 16,000 feet.
Joshi said the security set-up and infrastructure of both sides was also in sharp contrast.
"The terrain is not as harsh on their side. And they have built roads and outposts right up to the border. On the Indian side in the northeast, supplies have to be sent to some posts on mules and by porters, because even the nearest road is 90 kilometres away," he said.
Some posts are "air-maintained" by aircraft ferries. But for many others, cans of kerosene oil, food packets and letters for the soldiers are transported through the treacherous mountain paths to the border.