India said its warplanes struck a militant training camp inside Pakistan on Tuesday, killing "a very large number" of fighters, raising risk of conflict between the nuclear armed neighbors, though Pakistan officials denied there had been any casualties.
The airstrike near the town of Balakot, about 30 miles from the frontier was the deepest cross-border raid launched by India since the last of its three wars with Pakistan in 1971.
Pakistan condemned the Indian action and said it would respond at a time and place of its choice.
The airstrikes, according to the Indian government, hit a training camp of Jaish-e-Mohammed (JeM), the group that claimed credit for a suicide car bomb attack killed at least 40 Indian paramilitary police in Kashmir on Feb. 14. The action was ordered as India said it had intelligence that Jaish was planning more attacks.
"In the face of imminent danger, a preemptive strike became absolutely necessary," Foreign Secretary Vijay Gokhale told reporters.
"The existence of such training facilities, capable of training hundreds of jihadis could not have functioned without the knowledge of the Pakistani authorities," Gokhale said.
Pakistan denies harboring JeM, a primarily anti-India group that forged ties with al-Qaeda and has been on a UN terror list since 2001. In December 2001, Jaish fighters, along with members of another Pakistan-based militant group, Lashkar-e-Taiba, launched an attack on India's parliament, which almost led to a fourth war.
China, Pakistan's long-time ally, urged both countries to exercise restraint as tensions rose to the highest in years.
"We hope that India and Pakistan can exercise restraint, and take steps that are conducive to stabilizing the regional situation and improving bilateral ties, rather than the opposite," Foreign Ministry spokesman Lu Kang told a daily news briefing in Beijing.
Gokhale said "a very large number" of militants were killed in the strikes by French-made Mirage 2000 jets on a Jaish training camp near Balakot, a town in Pakistan's Khyber Pakhtunkhwa province.
The commander of the camp was Maulana Yusuf Azhar, a brother-in-law of JeM leader Masood Azhar, Gokhale said.
A senior Indian government source said that 300 militants had been killed in the strikes and that the warplanes had ventured as far as 50 miles inside Pakistan. But no evidence was immediately provided to back up the claims of militant casualties.
"I want to assure you our country is in safe hands," Prime Minister Narendra Modi told a cheering political rally in western India hours after the raid.
"I won't let the country down," said Modi, who faces a tight election in coming months.
There has been mounting impatience in India to avenge the Feb.14 attack, which was the most deadly seen in Kashmir during an insurgency that has last three decades, and as news of the raid broke, celebrations erupted across the country.
Pakistan's top civilian and military leaders rejected India's comments that it had struck "terror camps" inside Pakistan, vowing to prove wrong India's claims and warning that it would retaliate against Indian aggression.
Pakistan's National Security Committee (NSC), comprising top officials including Prime Minister Imran Khan and army chief Qamar Javed Bajwa, said in a statement that it "strongly rejected Indian claim of targeting an alleged terrorist camp near Balakot and the claim of heavy casualties."
The statement said Khan would "engage with global leadership to expose irresponsible Indian policy". It also warned that "Pakistan shall respond at the time and place of its choosing" to Indian aggression.
Earlier the Pakistan military said its own warplanes had chased off the Indian aircraft before they could inflict any real harm. A spokesman said the Indian warplanes dropped their "payload" in a forested area, causing no casualties and no serious material damage.
"Indian aircraft intruded from Muzaffarabad sector," Pakistani military spokesman Maj. Gen. Asif Ghafoor said on Twitter, referring to an area in the Pakistan-held part of Kashmir.
Ghafoor said the intruders faced a "timely and effective response from Pakistan Air Force," and "released payload in haste, while escaping, which fell near Balakot."
"No casualties or damage," he tweeted.
Ghafoor also posted four pictures of the alleged site, purportedly showing a bomb crater in a forest area but no serious damage.
Pakistani villagers in the area where the Indian jets struck said they heard four loud bangs in the early hours of Tuesday but reported only one person was wounded.
"We saw fallen trees and one damaged house, and four craters where the bombs had fallen," said Mohammad Ajmal, a 25-year-old who visited the site.
Indian television networks reported the airstrikes took place at 3:30 a.m. and involved a dozen Mirage fighter planes backed up by Israeli-equipped Airborne Warning and Control Systems (AWACS) aircraft that patrolled on India's side of the border.
Balakot is about 30 miles from Line of Control (LoC), the ceasefire line that is the de facto border in Kashmir, a Himalayan region that has been the cause of two of the three wars India and Pakistan have fought since the end of British colonial rule in 1947.
Analysts have alleged Pakistani militants have their training camps in the area, although Pakistan has always denied the presence of any such camps.
Mohammed Iqbal, a resident of Mendhar, a long way further south on the Indian side of the LoC, told Reuters that he heard jets flying through the night.
Shelling across the LoC has occurred frequently over the past few years but airspace violations by jets are extremely rare.
Following another large attack on Indian security forces in Kashmir in 2016, India said its troops crossed the LoC to carry out a "surgical strike" on suspected militant camps in Pakistan Kashmir. Islamabad denied anything serious occurred.
By Drazen Jorgic and Sanjeev Miglani/Reuters
Additional reporting by Asif Shahzad, Fayaz Bukhari, Neha Dasgupta, Nidhi Verma, and Ben Blanchard in Beijing; Writing by Alasdair Pal and Sanjeev Miglani; Editing by Simon Cameron-Moore.