“The Taliban don’t want peace, because they think they can win the war,” said the embattled governor of Baghlan Province, Abdul Hai Nimati, at his office here in Pul-i-Kumri. “If it goes on like this, they’re going to win.”

Appointed by President Ashraf Ghani, Mr. Nimati is a former jihadi commander who fought the Soviets and the Communist government during the 1980s and 1990s. “Back in those days, we had all the advantages of fighting a guerrilla war that the Taliban have now,” he said, almost wistfully. “We have to defend everywhere, and they can attack anywhere.”

The figure of 400 Afghan soldiers and police officers killed last week leaked out of a meeting last weekend between Gen. Austin Scott Miller, the new American military commander, and Western diplomats in Kabul, according to two of those present, who spoke on condition of anonymity because the meeting was meant to be off the record.

Asked about the meeting, the American military spokesman, Col. Dave Butler, did not specifically address the number killed last week, instead saying, “General Miller’s remarks are not accurately reflected by your sources’ recollection.” He added: “He was reflecting on Afghan sacrifice over a several-week period. He was relaying a sense of urgency to the team and encouraging focus on the mission.”

The quiet acknowledgment of higher casualties is coming at a time of alarm about the Taliban’s gains across Afghanistan. More districts than at any time since 2001 — including some provincial capitals — have fallen under threat or outright control by the insurgents over the past year.