Pakistan closed its air space for Indian airlines and rejected New Delhi's suspension of a critical water sharing treaty on Thursday in retaliation for India's response to a deadly Islamist militant attack on tourists in Indian Kashmir.

The spray of gunfire at tourists Tuesday in a scenic, mountain-ringed valley was the worst assault in years targeting civilians in the restive region.

Pakistan warned India on Thursday that it was committing an "act of war" by suspending a landmark water-sharing treaty in response to a deadly terror attack in Indian-controlled Kashmir. The threat from Pakistan Prime Minister's Office followed a number of diplomatic measures imposed by New Dehli on Islamabad as tensions flare between the neighboring nuclear powers.