India has formally protested to Beijing over irregularities in visa procedures for citizens from its troubled Kashmir region, amid mounting friction between the two Asian powers.

The diplomatic spat over the visas came as P.V. Naik, India’s air force chief, said that India was undertaking an upgrade of its defence infrastructure in the north-eastern state of Arunachal Pradesh, a disputed territory that Beijing refers to as “southern Tibet” and claims as its own.