Pakistan says its air force shot down two Indian fighter jets over the disputed border region of Kashmir, in a significant escalation of the crisis between the two nuclear-armed powers.

India confirmed the loss of one plane and said it shot down a Pakistani jet as it responded to the incident.

The confrontation came a day after India said it launched airstrikes in Pakistan territory in the first such incursion by Indian Air Force planes since the India-Pakistan war of 1971.

Pakistan’s chief military spokesperson, Maj. Gen. Asif Ghafoor, claimed two Indian jets were downed in Wednesday’s operation. One fell inside Pakistan-controlled Kashmir, while another went down in the Indian-controlled region of Kashmir, he said on Twitter.

Ghafoor initially claimed two Indian pilots were arrested and said one was being treated for injuries in a military hospital. But on Twitter later Wednesday, he said only one was in military custody.

India confirmed the Pakistan strikes but said that it had lost only one aircraft. One pilot was missing, it said. India did not say where its plane went down. Indian Foreign Ministry spokesperson Raveesh Kumar said an Indian air force plane retaliated, shooting down a Pakistani jet, which fell on the Pakistan side of the border.

Pakistan later released what it said was a video of the detained Indian pilot, identifying him as Wing Comd Abhinandan. India called the move a “vulgar display” and “unprovoked act of aggression” that “violates all norms of international humanitarian law.”

The escalating tensions come at a politically crucial time for India, which is scheduled to hold national elections by the end of May.

Pakistan closed its airspace for a time on on Wednesday. A number of Indian airlines announced the suspension of flights to several Indian airports. Flights later resumed.

Pakistan’s Prime Minister, Imran Khan said was “retaliation” for Tuesday’s incursion by India. In a national address, Khan said that that both sides could not afford “miscalculations” and that any further escalation would be beyond the control of him and Indian Prime Minister Narendra Modi.

Earlier, Pakistan’s Foreign Ministry said that Islamabad had carried out aerial strikes on “nonmilitary targets” across the line of control (LoC) from within Pakistani airspace, claiming to have avoided “human loss and collateral damage.” It accused India of “carrying out acts of terror in Pakistan.”

The purpose of the strike was to demonstrate the country’s self-defense capabilities, the Foreign Ministry said. “We have no intention of escalation, but are fully prepared to do so if forced into that paradigm. That is why we undertook the action with clear warning and in broad daylight,” the statement said.

Britain’s Prime Minister Theresa May called for “restraint on both sides,” telling Parliament Wednesday that the UK was working closely with international partners to “de-escalate tensions.”

US Secretary of State Mike Pompeo spoke with his counterparts in India and Pakistan, and also urged restraint.

‘Not a military operation’

Kashmir, a largely mountainous region located between India and Pakistan, has been bitterly contested by both countries following partition in 1947, leading to three wars and numerous other skirmishes.

Skirmishes along the Line of Control have escalated since the alleged Indian airstrikes. On Tuesday, Pakistan troops opened fire at 15 places across the line in Jammu and Kashmir, injuring five Indian soldiers, army spokesperson Devender Anand told CNN.

Earlier on Wednesday, Indian Foreign Affairs Minister Sushma Swaraj said the country does not want “further escalation” with Pakistan.

Speaking at a foreign ministers meeting between Russia, India, and China in Wuzhen, China, on Wednesday, Swaraj said Tuesday’s strike was “not a military operation” but “a preemptive strike against the terrorist infrastructure of Jaish-e-Mohammed.”

India blames the militant group Jaish-e-Mohammed (JeM) for a suicide car bomb attack in Indian-controlled Kashmir, which killed 40 Indian paramilitary soldiers on February 14.

India had previously said that Pakistan had a “direct hand” in the attack — the deadliest on security forces since the beginning of the insurgency in the late 1980s. Pakistan has vehemently denied having a role in the incident.

Swaraj said that Tuesday’s pre-dawn operation was launched because of the “continuing refusal of Pakistan to acknowledge and act against terror groups on its territory.”

The military action was based on “credible information” that militants were planning other attacks in various parts of the country, Swaraj said.

In its Foreign Ministry statement Wednesday, Pakistan said that “India has been trying to establish what they call ‘a new normal’ a thinly veiled term for doing acts of aggression at whatever pretext they wish on a given day. If India is striking at so called terrorist backers without a shred of evidence, we also retain reciprocal rights to retaliate against elements that enjoy Indian patronage while carrying out acts of terror in Pakistan.”

Harsh V Pant, a professor in international relations at King’s College London, told CNN that for the past few decades the Indian government had chosen not to retaliate after terror attacks in Kashmir.

But India is now at a point where it is choosing to escalate the situation, adding that India’s military action follows public anger over the attack.