India is retaliating against Pakistan in major ways as tensions soar in the wake of the Tuesday terrorist attack on Indian-Controlled Kashmir, which killed 26 tourists in the picturesque region.

Not only has India closed its border to Pakistan, declaring that no visas will be given to Pakistanis, but the Indian government has downgraded its diplomatic ties with Islamabad and suspended a crucial water treaty. Pakistani visa holders in India have also been ordered leave the country within 48 hours.

The water issue will could impact hundreds of millions of people on both sides of the border, as the 1960 Indus Water Treaty delineates how water is distributed and used from six rivers that flow through both countries, starting in disputed regions of the Himalayas in the north.

The decision was made in a meeting chaired by India's Prime Minister Narendra Modi, who cut short a trip to Saudi Arabia. All Pakistan military advisers who were previously cooperating with their Indian counterparts have also been given a week to leave.

During the terror attack on the tourist destination in the Baisaran Valley men were separated from women and children by armed militants which had descended on the area. The men, all civilians, were then asked their names before being executed at close range. 

This apparently was to confirm that they were Hindus. India has alleged that this was a Pakistan-backed massacre conducted by Islamic extremists due to the sectarian nature of the attack. Islamabad has long been accused of harboring Islamic terror groups along the disputed Jammu and Kashmir border region.

India’s Foreign Secretary Vikram Misri specifically charged Wednesday press conference that "cross-border linkages of the terrorist act" had been "brought out" - in a clear reference to Pakistan. Authorities have identified that 25 victims were Indian, and one a Nepali citizen. 

Pakistan has firmly rejected it had anything to do with the massacre, instead saying that terrorism in India was "homegrown". Pakistan's Defense Minister Khawaja Asif said "This is the result of a Hindutva [Hindu nationalist] government exploiting and killing religious minorities, including Christians and Buddhists," He described to a Pakistan news service this was the result of "homegrown rebels." 

Accounts by the women survivors, graphic images of their husbands slain:

Pakistan is taking reciprocal measures:

Pakistan on Thursday also announced the closure of its airspace to India; suspended all trade with the country; suspended with immediate effect all visas issued to Indian nationals under an exemption scheme; reduced to 30 the number of diplomats in the Indian High Commission in Islamabad; and asked Indian defense, naval and air advisers to leave Pakistan before April 30.

India's attempts to link the attack with Pakistan are "frivolous, devoid of rationality and defeat logic," Islamabad said, describing India's sweeping diplomatic measures as "unilateral, unjust, politically motivated, extremely irresponsible and devoid of legal merit."

The two rival nuclear-armed powers have fought no less than three wars over the status of the Muslim-majority Kashmir region, given both sides claim it in its entirety - going back to 1947. 

As for India's cancelation of the landmark water treaty, Pakistan on Thursday is warning that India is committing an "act of war".

Pakistan's National Security Committee has declared that if India moves forward with suspending the Indus Water Treaty, which was carefully mediated by the World Bank, it "will be considered as an Act of War."

A relatively unknown group calling itself The Resistance Front claimed responsibility for the attack in a social media post. It blamed "outsiders" who settled the region and caused a "demographic change" - strongly suggesting the terror attack was tied to Indian claims over the disputed region. Indian military and police units are still searching for the suspects, and sketch artists have issued renderings of the attackers based on survivors' accounts.