India says it launched air strikes against Kashmiri militants in Pakistani territory in a major escalation of tensions between the two countries.
A top Indian minister said strikes targeted a training camp of the Jaish-e-Mohammad (JeM) group in Balakot.
Pakistan said it scrambled fighter planes in response.
Relations between the nuclear-armed neighbours have been strained since a suicide attack earlier this month that killed more than 40 Indian troops.
India accuses Pakistan of allowing militant groups to operate on its territory and says it played a role in the 14 February attack - claims that Pakistan denies.
Tuesday's air strikes are the first launched across the line of control - the de facto border that divides India-administered Kashmir from Pakistan-administered Kashmir - since a war between the two countries in 1971.
Indian Foreign Secretary Vijay Gokhale told a news conference that the strikes had killed a "large number" of militants, including commanders, and had avoided civilian casualties.
"Credible intel [intelligence] was received that JeM was planning more suicide attacks in India. In the face of imminent danger, a pre-emptive strike became absolutely necessary," he said.
Pakistan's army spokesman Major General Asif Ghafoor said the strikes caused no casualties. He tweeted that the Indian jets were forced to make a "hasty withdrawal" and dropped their payload in an open area.
The latest incident follows the suicide attack on an Indian security convoy in Pulwama, in Indian-administered Kashmir, earlier this month.
Analysts say the exact location of Balakot is unclear. Neither India nor Pakistan have officially confirmed whether the strikes took place within Pakistan-administered Kashmir or if Indian planes crossed the international border and bombed inside Pakistan itself.
But residents in several towns in Pakistan's Khyber Pakhtunkhwa province told BBC Urdu they were woken by loud explosions early on Tuesday.