The shift of the defenders to a regimental base outside the district center meant the district had been conceded to the Taliban, Mr. Shakir said.

Captain Salvin, the United States military spokesman, said that the American military had helped move Afghan soldiers by airlift to the new district center and that everyone had been relocated safely.

“Excessive damage by the Taliban to the area in the bazaar made it impossible for the people to see the government leaders and made it difficult to provide necessary services,” he said. “Once that was complete, the U.S. assisted in destroying the buildings that were no longer usable and also destroyed inoperable vehicles that were left in place so that they would not be a safety hazard.”

The Taliban had long dominated most territory in Sangin except for the district center, which was home to the government and police headquarters as well as the army base. According to Mr. Shakir, the insurgents now hold seven of Helmand Province’s 14 districts; in five of the others, he said, the government holds only the district centers. Only two districts and the provincial capital, Lashkar Gah, are completely under government control, he said.

Several of Helmand’s districts have repeatedly changed hands, and it was possible that could happen in Sangin as well. But the Taliban have been determined to take the district, fighting almost constantly over it for the past eight years, and analysts said they would be unlikely to give it up easily.

In 2009, Sangin was the responsibility of the British Army and Royal Marines, which suffered a total of 106 deaths there, out of 455 British losses for the country’s entire time in Afghanistan. Hamid Karzai, the president at the time, and American military commanders expressed dissatisfaction with the British record, and the United States Marines were brought in to replace them. Twenty were killed in Sangin in the first 90 days of their deployment.

By 2013, as Western troops reduced their numbers in Afghanistan and began transferring authority to Afghan forces in Helmand, the Taliban launched an offensive to retake Sangin, killing 120 Afghan police officers and soldiers that summer. By the spring of 2014, the last American Marines left Sangin and turned it over to Afghan forces. That summer, another Taliban offensive killed 230 Afghan police officers and soldiers, and wounded more than 400 — again, just in Sangin.