Following Tuesday’s murder by terrorists of 26 tourists at a mountainous resort in Indian Kashmir, New Delhi is imposing strong diplomatic sanctions on Pakistan, while Islamabad is contemplating counter measures. Are the two nuclear-armed countries now verging on a hot war?

“Hindu nationalists are pressuring Modi to respond strongly, but I’m not sure the prime minister is eager to wage an all-out war,” a former Western diplomat at New Delhi who keeps ties with Indian officials tells the Sun. Anger in India over Tuesday’s attack, though, is boiling.  Mr. Modi might need to up the ante in confronting Pakistan, after skirmishes between the countries have been at a low ebb in recent years.  

India’s foreign secretary, Vikram Misri, announced several measures Wednesday, including downgrading diplomatic relations, expelling Pakistani diplomats, and recalling Indian officials from Islamabad. Pakistani military attaches at New Delhi were declared personae non grata. Pakistani tourist visas have been canceled and border crossings are shut. Bilateral treaties, including on sharing the Indus river’s waters, are suspended.

For now, New Delhi’s announced measures are confined to the diplomatic arena. On Thursday, India’s defense minister, Rajnath Singh, is scheduled to lead a meeting of all government officials, including representatives from all parties in the country, to contemplate further measures. 

At Islamabad, Prime Minister Sharif will convene the Pakistani national security committee “to respond to the Indian government,” the foreign minister, Ishaq Dar, announced. Pakistan is entangled in several political crises, including the imprisonment of a former premier, Imran Khan, who is widely seen as the country’s most popular politician. Will internal turmoil prevent an escalation in relations with India? 

Indian authorities arrested at least 1,500 people across Jammu and Kashmir following Tuesday’s gunning down of tourists at the Pahalgam area, known as the “Switzerland of India.” The killing of at least 25 Indians and one Nepali man was the worst terrorist attack in India in recent years. A little-known group, calling itself the Kashmir resistance, took responsibility on Wednesday.  

The faction, whose gunmen have reportedly ensured that victims were non-Muslims before firing at them, is widely seen as an offshoot of Pakistan-based groups backed by Islamabad’s security agencies. Those include Lashkar-e-Taiba and Hizbul Mujahideen. It is unclear what prompted the deadly terror attack, which followed a long period of relative calm in the disputes between Pakistan and India over control of Kashmir.  

The attack “deliberately targeted Hindu tourists, segregated them, and then shot them at a point blank range,” the Hindu Times executive editor, Shishir Gupta, told a television interviewer. It was orchestrated by Pakistan “to humiliate India,” he added. “Mark my words, India will retaliate.”  

President Trump called Mr. Modi on Tuesday. Vice President Vance departed India Wednesday following a four-day tour, and said he too spoke with the premier. “Obviously, we’re providing whatever assistance and help we can provide to the government, to the people of India,” Mr. Vance said. 

Sympathy also poured in from around the world, as Italian, French, British, German, and Arab leaders — as well as Israelis, who are increasingly allied with India — called to express support and offer assistance. Notably, Communist China “strongly condemns this attack,” the foreign ministry spokesman of Pakistan-allied Beijing, Guo Jiakun, said Tuesday. 

The unified response is raising hopes among world diplomats that a hot war could be prevented. Can Mr. Modi, though, put a cap on Indian anger in response to a massacre widely seen as orchestrated by the unstable neighbor across the border?