KOHAT, Pakistan — Niaz Bibi’s son disappeared into the night, whisked away by Pakistani soldiers who accused him of being a Taliban fighter. For 18 anguishing months, she could find no word of his fate. Then she got a phone call.

“Come to Kohat prison,” said the man on the other end. “Tell nobody.”

At the prison, in northwestern Pakistan, she was directed to a separate, military-run internment center where her son, Asghar Muhammad, was brought to her. They touched hands through a metal grill, and she wept as he reassured her that he would be home soon.

But when the phone rang again, one month later, an official delivered crushing news. “Your son is dead,” he said. “Come collect his body.”

Mr. Muhammad was one of dozens of detainees who have died in military detention in Pakistan in the past year and a half, amid accounts of torture, starvation and extrajudicial execution from former detainees, relatives and human rights monitors. The accusations come at a time when the country’s generals, armed with extensive new legal and judicial powers, have escalated their war against the Pakistani Taliban by sweeping into their strongholds and detaining hundreds of people.