New Delhi accuses Islamabad of backing the deadliest attack in years on civilians in Indian-administered Kashmir on April 22, in which 26 men were killed.

Islamabad has rejected the charge, and both countries have since exchanged gunfire in Kashmir, diplomatic barbs, expelled citizens and ordered the border shut.

Pakistan closed its airspace to Indian aircraft on April 24, while India took a similar measure on Wednesday evening, with the ban to last until May 23, the government notice said.

The notice to air operators said that Indian airspace was not available for Pakistani registered or leased aircraft -- "including military flights".

Indian Prime Minister Narendra Modi gave the military "complete operational freedom" to respond to the attack during a closed-door meeting on Tuesday, a senior government source told AFP.

Pakistan's government has denied any involvement in the shooting and vowed that "any act of aggression will be met with a decisive response".