Though India and Pakistan routinely shell each other across what is known as the Line of Control, this is the first time in years that either side has deployed warplanes to fly across it.

Western security officials have raised questions about the existence of a large-scale training camp, saying that Pakistan no longer runs such camps and that militant groups are spread out in small groups around the country.

Analysts and diplomats in New Delhi said the targets of the Indian airstrikes were unclear, as any terrorist groups operating along the border would have cleared out in recent days after Prime Minister Narendra Modi of India vowed retaliation over the Kashmir attack.

Residents have also fled the area as hundreds of Kashmiris have been arrested and India has moved more troops into the region.

The Indian attack is likely to draw a response from Pakistan, analysts say.

“The Pakistanis are bound to react, conventionally and not through a proxy like a militant group,” said Rahul Bedi, an analyst at the London-based Jane’s Information Group, which tracks the defense industry. “Where they react and when is something that only Pakistanis know. This is a dangerous situation, as this brinkmanship can escalate quickly.”

The American government has typically been a broker between India and Pakistan, conducting shuttle diplomacy in similarly heated situations. But President Trump has taken a hard line on Pakistan while drawing closer to India since coming to office in 2017. Observers fear the situation may escalate further in the absence of a third nation tamping down tensions.

Early last year, Mr. Trump cut some $1.3 billion in military assistance to Pakistan because of the country’s support of terrorist groups. Pakistan’s military denies that it engages terrorist groups to achieve its defense and foreign policy objectives.