The move indicated the troops were preparing the network for the future, the officials said, despite both countries being engrossed in discussions to dissipate a deadlock in the region. The connection would allow forward troops to contact bases in the rear.
The cables were spotted to the south of Pangong Tso lake in the Himalayan region of Ladakh, a senior government official said.
Troops from both sides have been stuck in a standoff along a 70 km-long front to the south of the lake.
Both sides are equipped with tanks and aircraft.
On Monday, a third Indian official said there had been no critical retractions or reinforcements from either nation since the foreign ministers of both countries met last week.
He said: “It is as tense as earlier.”
China India war fears surge as Chinese army lays communication cables in standoff region
On the lake’s southern bank troops from both sides are only separated by a few hundred meters in some areas.
The first official said: “Our biggest worry is that they have laid optical fibre cables for high-speed communications.”
“They have been laying optical fibre cables on the southern bank at breakneck speed.”
The second official added that around a month ago similar connections were spotted by Indian intelligence bureaus to the north of the Pangong Tso lake.
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An Indian Air Force aircraft is seen against the backdrop of mountains surrounding Leh, the joint capital of the union territory of Ladakh
Antoine Levesques, research partner for South Asia at the International Institute for Strategic Studies (IISS), said that the lake does not have much military importance to either country, but they have increased the patrols and development regardless.
Mr Levesques said: “diplomats had refrained from publicly and specifically discussing the situation at Pangong Tso lake.
“But it remains one location where successive rounds of military-led talks have failed to result yet in impactful or visible de-escalation and disengagement witnessed in other hotspots.”
He added that China has strategic interests in dominating the area of the lake.
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He said: “As the site of a bloody tactical battle in 1962 which India lost, before losing that year’s short conflict altogether, Pangong Tso carries considerable symbolic value.”
The tension between both nuclear-armed powers alarmed western countries after earlier this month, China accused Indian troops of illegally trespassing on Chinese territory in the Himalayas.
About the purported breach, Chinese Foreign Ministry spokeswoman Hua Chunying said: “The Indian side has severely undermined China’s territorial sovereignty, breached bilateral agreements and important consensus, and damaged peace and tranquillity in the border areas, which runs counter to the recent efforts made by both sides for de-escalation of tensions on the ground.”
Writing last month for the Carnegie Endowment for International Peace, analysts Toby Dalton and Tong Zhao defined the confrontation as “the gravest military confrontation the two nuclear powers have faced in fifty years.
Indian demonstrators shout anti Chinese slogans as they burn Chinese flags and poster depicting Chinese President Xi Jinping
“If ties between the two powerful neighbours are indeed entering a more sharply competitive era, a crucial question arises: will nuclear weapons play a more prominent role as each country seeks to shape each other’s behaviour?
“So far, despite both countries possessing nuclear arsenals and periodic border dispute flare-ups, nuclear deterrence has not been a main or even secondary feature of their relationship.
“Unlike India-Pakistan or China-US relations, in which the potential for nuclear weapons use has hung over their military interactions, China-India relations have been tempered by decades of stable political ties and shared economic priorities.
“Threat perceptions between Beijing and New Delhi have concentrated instead on their disputed borders in the Himalayas and their suspicions about the strategic relations each has built with the other’s main adversary—China with Pakistan and India with the United States.”