India has accused Chinese troops of meticulously preparing an attack on its soldiers on the treacherous Himalayan border, claiming they erected a tent on the Indian side, dammed a river, brought in machinery and then lay in wait with stones and batons wrapped in barbed wire. The incident on Monday night, in which 20 Indian soldiers died and 76 were injured, was the worst violence between India and China for 45 years. China has not said whether it sustained any casualties. Ten Indian soldiers who were reportedly captured by Chinese troops during the attack were back in India on Thursday night. China said it had not seized any Indian personnel. Both sides continue to blame the other for the clash. China is now claiming sovereignty over the Galwan valley in Ladakh, where the attack happened, and has accused Indian troops of three times crossing into its territory. “The responsibility entirely lies with Indian side,” said Zhao Lijian, a spokesman for the Chinese ministry of foreign affairs. India accused China of carrying out a “premeditated and planned action” on its side of the border. Satellite images of the Galwan valley taken by Planet Labs, an imaging company, in the days before the clash appear to show increased activity on the Chinese side, including the damming of a river and the movement of troops and machinery close to the disputed and poorly defined border. The Australian Strategic Policy Institute said its analysis of satellite images found there was “evidence that strongly suggests People’s Liberation Army forces have been regularly crossing into Indian territory temporarily on routine patrol routes”. Indian officials said commanders from the Indian and Chinese sides had met on 13 June and agreed to each retreat back two kilometres in the Galwan valley and Pangong Lake area. But rather than retreating, the officials said, Chinese troops erected a tent in disputed territory close to what is known as Patrolling Point 14. They said India’s 16 Bihar Regiment, led by Col Santosh Babu, dismantled the structure in an attempt to push back the PLA troops. According to accounts given to the Hindu newspaper, when Babu and his troops later approached the Chinese side to challenge the refusal to retreat, they were ambushed by PLA forces on the steep mountain precipice. The Chinese allegedly unblocked the dammed river, releasing a rush of water to destabilise Indian soldiers, and they attacked with stones and makeshift spiked weapons. Indian troops retaliated, it was reported, and reinforcements were summoned on both sides until there were upwards of 600 soldiers in hand-to-hand combat in the dark and icy conditions. No shots were fired. There were reports that the Indian soldiers were unarmed, but India’s external affairs minister, Subrahmanyam Jaishankar, said: “Let us get the facts straight. All troops on border duty always carry arms, especially when leaving post. Those at Galwan on 15 June did so.” Due to the treacherous conditions, many of the bodies of the Indian soldiers could not be retrieved until the next morning, by helicopters working with troops and border police. The injured were taken to hospitals in the Ladakh city of Leh. India and China have agreed to continue the process of disengagement that was first agreed on 6 June, and discussions are ongoing through political and diplomatic channels. Army generals from both sides have also had three days of talks at Patrolling Point 14. However, the Indian army and air force in Ladakh remain on high alert. India’s prime minister, Narendra Modi, held a meeting with all political party leaders on Friday evening to discuss the situation. China has doubled down on its claim over the Galwan valley. “Based on the principle of historic rights, China has jurisdiction over the valley area,” Zhang Yongpan, a research fellow of the Institute of Chinese Borderland Studies, told the Global Times, a government mouthpiece, on Thursday. In an editorial published on Friday, the Global Times claimed the Indian soldiers died because they were exposed to freezing temperatures, not because they were beaten or pushed off the ridge. “China and India have always had different understandings of the LAC, but to control the situation on the border, neither country should act first,” the editorial said. “Indian troops broke the deal. Then, 17 Indian troops died because they were exposed to freezing temperatures in the high altitude after being injured.”