BALSOO, Kashmir — It was well past midnight in the village of Balsoo when Numan Ashraf Bhat’s phone lit up with an urgent WhatsApp message: “Umar surrounded by forces.”

Umar Majid Ganai, one of the area’s most wanted militants, had built a loyal youth following in Kashmir, a Himalayan region disputed between India and Pakistan where violence has claimed tens of thousands of lives. Numan, a gangly 16-year-old, was one of his most enthusiastic supporters — all of the photos downloaded on his phone were of Mr. Ganai.

So when Numan learned last month that Mr. Ganai was holed up in a tiny hamlet, Indian security forces closing in, he jumped on his motorbike and sped through the biting cold to reach the house where several militants were trapped.

Hundreds of Kashmiri civilians had already gathered. They were forming a protective ring to block Indian officers from advancing, part of a new and often fatal development in the decades-long struggle over Kashmir.