Indian Prime Minister Narendra Modi vowed on Thursday to pursue, track and punish terrorists and their backers in a strong reaction to a deadly attack on tourists in the occupied Kashmir valley, where police have identified three of the gunmen.

At a speech in India's eastern state of Bihar, Modi folded his hands in prayer in remembrance for the 26 men who were shot and killed in a meadow in the Pahalgam region of India-held Kashmir, exhorting thousands gathered at the venue to do the same.

"We will pursue them to the ends of the earth," Modi said, referring to the attackers, without referring to their identities or naming any country.

His comments are, however, bound to further inflame ties between the nuclear-armed rivals after India downgraded ties with Pakistan late on Wednesday, suspending a six-decade-old water treaty and closing the only land border crossing between the neighbours.

Power Minister Awais Leghari called the suspension of the Indus Waters Treaty "an act of water warfare; a cowardly, illegal move".

Police in Indian Kashmir published notices on Thursday naming three suspected militants "involved in" the attack, and announced rewards for information leading to their arrest. Two of the three suspects were alleged to be Pakistanis, the notices said. They did not say how the men were identified.

Indian Foreign Secretary Vikram Misri said on Wednesday a cabinet committee on security was briefed on the cross-border linkages of the attack, the worst on civilians in the country in nearly two decades.

Misri, the top diplomat in India's foreign ministry, did not offer any proof of the linkages or provide any more details.

New Delhi will also pull out its defence advisers in Pakistan and reduce staff size at its mission in Islamabad to 30 from 55, Misri said.

India has summoned the top diplomat at the Pakistan embassy in New Delhi, local media reported, to give notice that all defence advisers in the Pakistani mission were persona non grata and given a week to leave, one of the measures Misri announced.

Modi has also called for an all-party meeting with opposition parties to brief them on the government's response to the attack.

Protest at embassy

Dozens of protesters gathered outside the Pakistan embassy in New Delhi's diplomatic enclave on Thursday, shouting slogans and pushing against police barricades.

In Islamabad, Prime Minister Shehbaz Sharif held a meeting of the National Security Committee to discuss Pakistan's response, Foreign Minister Ishaq Dar said in a post on X.

The Indus treaty, mediated by the World Bank and signed in 1960, regulated the sharing of waters of the Indus River and its tributaries between India and Pakistan. It has withstood two wars between the neighbours since then and severe strains in ties at other times.

Diplomatic relations between the two countries were weak even before the latest measures were announced as Pakistan had expelled India's envoy and not posted its own ambassador in New Delhi after India revoked the semi-autonomous status of Kashmir in 2019.