The Indian hits on targets in Pakistan's most populous province of Punjab on Wednesday were the first since their last full-scale war more than half a century ago, triggering fears of a further escalation of military hostilities.
India said it struck nine Pakistani "terrorist infrastructure" sites, some of them linked to an attack by Islamist militants on Hindu tourists that killed 26 people in Indian Kashmir in April.
India had earlier said two of three suspects in that attack were Pakistani nationals but had not detailed any evidence, while Pakistan denied it had anything to do with the killings.
Islamabad said six Pakistani locations were targeted, and none of them were militant camps.
At least 26 civilians were killed and 46 injured, the Pakistan military said.
Indian forces attacked facilities linked to Islamist militant groups Jaish-e-Mohammed and Lashkar-e-Taiba, Indian military representatives told a briefing in New Delhi.
The strikes targeted "terrorist camps" that served as recruitment centres and indoctrination centres, and housed weapons and training facilities, the representatives said.
"Intelligence and monitoring of Pakistan-based terror modules showed that further attacks against India were impending, therefore it was necessary to take pre-emptive and precautionary strikes," Indian Foreign Secretary Vikram Misri, the top official in its external affairs ministry, told the briefing.
The joint briefing by the Indian military and foreign ministry listed past attacks in India blamed on Pakistan, with Misri saying Pakistan had not done anything to "terrorist infrastructure" there after the attack on Kashmir tourists.
Pakistan said Indian missiles hit three sites and a military spokesperson said five Indian aircraft had been shot down, a claim not confirmed by India.
However, four local government sources in Indian Kashmir told Reuters that three fighter jets had crashed during the night, and the three pilots were hospitalised.
Islamabad called the assault a "blatant act of war" and said it had informed the UN Security Council that Pakistan reserved the right to respond appropriately to Indian aggression.
Lieutenant General Ahmed Sharif Chaudhry, a Pakistan military spokesman, said Pakistan would "respond to this aggression at a time, place, and means of our own choice".
"We will take all the steps necessary for defending the honour, integrity and sovereignty of Pakistan, at all cost," he said.
The South Asian neighbours also exchanged intense shelling and heavy gunfire across much of their de facto border in the Himalayan region of Kashmir.
Hindu-majority India and Islamic Pakistan have fought two of their three wars since independence in 1947 over Muslim-majority Kashmir, which both sides claim in full and control in part.
Since a 2003 ceasefire, to which both countries recommitted in 2021, targeted strikes between the neighbours are extremely rare.
But analysts said the risk of escalation was higher than in the recent past due to the severity of India's attack, which New Delhi called "Operation Sindoor".
US President Donald Trump called the fighting "a shame" and added, "I hope it ends quickly."
The State Department said Secretary of State Marco Rubio spoke to both nations, urging them "to keep lines of communication open and avoid escalation".
UN Secretary-General Antonio Guterres called for maximum military restraint from both countries, a spokesperson said.
China, which neighbours both India and Pakistan, and Russia also called for restraint.
The shelling across the frontier in Kashmir killed 10 civilians in the Indian part of the region and at least six on the Pakistani side, officials said.
