NEW DELHI — Smiles rarely left the faces of the top leaders of India and China here on Thursday, but India’s new prime minister sent a tough message to his Chinese guest by pressing him for a resolution to a border dispute that has escalated abruptly.

A large contingent of Indian troops, which one official said numbered in the thousands, was mobilized Thursday to face an equivalent number of Chinese troops in Ladakh, Kashmir, a largely high-altitude, barren Himalayan landscape where jingoism and military conflict have dominated for decades.

Only India’s prime minister, Narendra Modi, could have ordered such a mobilization, said Mohan Guruswamy, a military analyst with the Observer Research Foundation.

The Chinese president, Xi Jinping, is in the middle of a three-day Indian visit that has been billed as the beginning of a great economic and political partnership. Several deals, including for high-speed trains and economic zones, had been promised at a total price tag that officials hinted could reach as much as $100 billion — nearly three times what Japan, China’s foremost Asian rival, recently promised to India.