Pakistan closed its air space for Indian airlines and rejected New Delhi’s suspension of a water sharing treaty on Thursday in retaliation for neighbouring India’s response to a deadly militant attack in the Indian-ruled part of Kashmir.

The announcement from the Pakistan Prime Minister’s Office followed a meeting of the National Security Committee, a day after India said there were cross-border elements to Tuesday’s attack, in which 26 men were shot dead by militants at a popular tourist destination.

Indian police published notices naming three militant suspects and saying two were Pakistanis, but New Delhi has not offered any proof of the linkages or shared any more details.

However, on Wednesday it downgraded ties with Pakistan, suspending a six-decade old treaty on the waters of the Indus river and closing the only land crossing between the neighbours.

Like India, Pakistan claims both the Indian- and Pakistani-ruled parts of Kashmir.

“Any threat to Pakistan’s sovereignty and to the security of its people will be met with firm reciprocal measures in all domains,” the Pakistani statement said.

It added that any attempt to stop or divert water belonging to Pakistan would be considered an act of war.