WASHINGTON — The Trump administration is urging American-backed Afghan troops to retreat from sparsely populated areas of the country, officials said, all but ensuring the Taliban will remain in control of vast stretches of the country.

The approach is outlined in a previously undisclosed part of the war strategy that President Trump announced last year, according to three officials who described the documents to The New York Times on the condition of anonymity. It is meant to protect military forces from attacks at isolated and vulnerable outposts, and focuses on protecting cities such as Kabul, the capital, and other population centers.

The withdrawal resembles strategies embraced by both the Bush and Obama administrations that have started and stuttered over the nearly 17-year war. It will effectively ensure that the Taliban and other insurgent groups will hold on to territory that they have already seized, leaving the government in Kabul to safeguard the capital and cities such as Kandahar, Kunduz, Mazar-i-Sharif and Jalalabad.

The retreat to the cities is a searing acknowledgment that the American-installed government in Afghanistan remains unable to lead and protect the country’s sprawling rural population. Over the years, as waves of American and NATO troops have come and left in repeated cycles, the government has slowly retrenched and ceded chunks of territory to the Taliban, cleaving Afghanistan into disparate parts and ensuring a conflict with no end in sight.