When Saudi Arabia and Pakistan signed a mutual defence agreement earlier this month, it was widely interpreted as a gesture of Muslim unity in a region roiled by crisis.

But its reverberations are already being felt among policymakers in Pakistan’s perennial rival India , threatening to complicate New Delhi’s delicate diplomatic balancing act in the Gulf.

The agreement, signed in Riyadh on September 17 , declares that aggression against either signatory “shall be considered aggression against both”.