In a statement, Mr. Cook said that Mr. Mansoor had “orchestrated multiple terrorist operations in Pakistan,” including the 2014 attack on the school in Peshawar, an attack on an air force base in 2015 and the January assault on Bacha Khan University in Charsadda that left at least 20 students and teachers dead.

“The United States maintains a robust counterterrorism partnership with Afghanistan and Pakistan, and we recognize the sacrifices made on behalf of our respective militaries to pursue terrorists for the sake of regional peace and security,” Mr. Cook said.

The attack on the Army Public School in Peshawar in 2014 was one of the deadliest and most shocking terrorist attacks in Pakistan’s history. A group of gunmen killed 148 people during an eight-hour rampage, at least 132 of whom were children.

In claiming responsibility, Mr. Mansoor said the attack had been retaliation for the continuing military operation against the group in the North Waziristan tribal region, which had long been a safe haven for local and foreign militants.

Pakistan had sought the United States’ assistance in locating Mr. Mansoor and others involved in the massacre, who were believed to be hiding in Afghanistan. High-ranking Pakistani Army and intelligence officials had also traveled to Kabul, the Afghan capital, seeking cooperation.