India on Tuesday launched airstrikes across its border with Pakistan in a military escalation after a terror attack in Kashmir left 40 Indian troops dead.

Pakistan immediately convened a meeting of its nuclear commanders and issued a thinly veiled nuclear threat to India.

The airstrike from India involved nuclear-capable aircraft and, according to India, killed up to 300 militants. B ut Pakistan said the Indian jets were chased off and killed no one.

With China closely backing Pakistan and the US supporting India, Pakistan and India's rivalry has long been seen as a potential flash point for a global nuclear conflict.

Both sides appear to be out for blood as gun fighting cracks off on the border and Indians around the country celebrate what they see as vengeance for the terror attack.

India on Tuesday launched airstrikes across its border with Pakistan in a military escalation after a terror attack in Kashmir left 40 Indian troops dead, and Pakistan immediately convened a meeting of its nuclear commanders.

Gun fighting on the ground broke out along India and Pakistan's de facto border after what Vipin Narang, an MIT professor and an expert on the two country's conventional and nuclear forces, called "India’s most significant airstrike against Pak in half a century."

The strikes happened after Indian Prime Minister Narendra Modi unleashed the military to respond however it saw fit after the terror attack, which India blames on Islamic militants based in Pakistan.

India and Pakistan, which have been engaged in a bitter rivalry for decades, have fought three wars over the disputed territory, and analysts are closely watching the crisis for clues about whether it could escalate from airstrikes to a heightened nuclear posture.

Pakistan denies any involvement in the terror attack but swiftly "took control" of the Jaish-e-Mohammed militant camp in question.

Read more: Pakistan readies military, hospitals for war with its nuclear rival India after Pulwama terror attack

Political map of the Kashmir region districts, showing the Pir Panjal Range and the Kashmir Valley. CIA via Wikimedia Commons

India said its airstrikes killed as many as 300 Muslim separatist militants, but it is unclear whether the attack had any effect. Pakistan said its air force scrambled fighter jets and chased India off, forcing the jets to hastily drop their bombs in an unpopulated area, and Pakistan's prime minister called India's claims "fictitious."

For the mission, India flew its Mirage 2000 jets, which it uses as part of its nuclear deterrence. The jets dropped more than 2,000 pounds of laser-guided bombs, according to News18.com. As a branch of India's nuclear forces, the Mirage 2000 fleet has some of the most ready aircraft and pilots, India Today reported.

The strike took place about 30 miles deep into Pakistan's territory in a town called Balakot, Indian Foreign Secretary Vijay Gokhale said at a press conference.

"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. The US has similarly accused Pakistan of harboring terrorists and backed India's right to self-defense after the terror attack.

Read more: India unleashes its military on Pakistan after a terror attack stoked the feud between the nuclear rivals

Maj. Gen. Asif Ghafoor, the spokesperson for Pakistan's military, said Pakistan successfully scrambled jets and scared off the incoming Indian Mirage 2000s. He also tweeted pictures of craters and parts of what could be Indian bombs.

"Payload of hastily escaping Indian aircrafts fell in open," Ghafoor said of the images. It's unclear if India hit their targets, actually killed anyone, or simply dropped fuel tanks upon leaving Pakistan.

India's airstrikes hit relatively close to Pakistan's prominent military academies and the country's capital, Islamabad, raising concern among the military that it's under the threat of further Indian strikes.

Pakistan's Hatf VII (Babur) missile takes off during a test in December 2007. Reuters stringer Pakistan's nuclear threat

At a press conference in response to the airstrikes, Ghafoor issued a veiled nuclear threat to India.

"We will surprise you. Wait for that surprise. I said that our response will be different. The response will come differently," Ghafoor said at a press conference.

Ghafoor added that Pakistan had called a meeting of its National Command Authority, which controls the country's nuclear arsenal.

"You all know what that means," Ghafoor said of the nuclear commanders' meeting in a press conference he posted to Twitter.

Read more: We ranked the world's nuclear arsenals — here's why China's came out on top

But India has nuclear weapons and means to deliver them, too. Additionally, both countries maintain large conventional militaries that have become increasingly hostile in their rhetoric toward each other.

Best case scenario? Conventional skirmishes

An Indian officer from the Indian Central Reserve Police Force. AP

India and Pakistan have fought three wars over the border and have nuclearized to counter each other's forces. With China closely backing Pakistan and the US supporting India, Pakistan and India's rivalry has long been seen as a potential flash point for a global nuclear conflict.

Reuters' Idrees Ali reported after the strikes that gunfights had broken out along Pakistan and India's border. The two countries have fought three wars over the disputed region of Kashmir, which both countries claim but administer only in part.

Both India and Pakistan now appear to be out for blood after the fighting. Reuters reported that all around India people were celebrating, and Modi praised the military as "heroes."

Meanwhile, Pakistan's denial that the airstrikes hit anything may give them some deniability and wiggle room to not respond with escalation, but hardliners within Pakistan will likely call for action.