Pakistan’s National Security Council (NSC) said it had authorized the country’s armed forces “to avenge” strikes by India, as powers including the U.S. and China—which borders both countries—urged the nuclear-armed neighbors to show restraint.

India launched airstrikes on Wednesday in “Operation Sindoor” targeting alleged terrorist infrastructure in Pakistan and Pakistan-controlled Jammu and Kashmir that it said was used as a launchpad for an attack on tourists near the town of Pahalgam on April 22.

Pakistan said the strikes had killed and injured civilians, including a woman and a child at a mosque that was hit. Pakistan’s NSC called the strikes “acts of war under international law.”

“In consonance with Article-51 of the UN Charter, Pakistan reserves the right to respond, in self-defence, at a time, place, and manner of its choosing to avenge the loss of innocent Pakistani lives and blatant violation of its sovereignty,” the NSC said in a statement on Wednesday.

“The Armed Forces of Pakistan have duly been authorized to undertake corresponding actions in this regard,” the statement said.

Pakistan responded immediately to the strikes with shelling into Indian-administered Kashmir, which India said killed several civilians. Pakistan also claimed it shot down several Indian military jets.

Following the strikes, there was a heavy exchange of fire that officials in each country said left more people dead.

Three planes fell onto villages in India-controlled territory, according to Indian police and residents, though it was not immediately clear if Pakistan downed them.

Tensions have soared between the nuclear-armed neighbors since an April attack in which gunmen killed 26 people, mostly Indian Hindu tourists, in India-controlled Kashmir, in some cases killing men before their wives’ eyes.

The three previous wars over Kashmir have each been bloody; the last one in 1999 killed more than a thousand Pakistani troops, by the most conservative estimates.

In the decades since, militant groups have fought Indian security forces, with violence killing tens of thousands.

The two countries have clashed multiple times, most recently in 2019 when India conducted airstrikes in Pakistan after it blamed Islamabad for a suicide car bomb attack in the region.

But those recent clashes did not explode into all-out war. Both sides are aware of the risks; since 1999, the two countries have worked to strengthen their militaries, including arming themselves with nuclear weapons.

How is the world reacting?
The strikes have raised global alarm and pleas for the two nations to prevent further escalation.

United Nations Secretary-General António Guterres voiced “deep concern” over India’s strikes, warning that the world “cannot afford a military confrontation” between the two nations.

The United States – which had urged restraint from both countries last week – said it was “closely monitoring developments,” according to a State Department spokesperson.

“We are aware of the reports, however we have no assessment to offer at this time,” the spokesperson said Tuesday. “This remains an evolving situation, and we are closely monitoring developments.”

The United Arab Emirates, China and Japan have also called for both sides to de-escalate.

A senior Indian government official told CNN that New Delhi had briefed its international counterparts on the steps it had taken – including the US, UAE, United Kingdom, Saudi Arabia and Russia.