SANGIN, Afghanistan — Some days, the Afghan soldiers worry that the mud walls around their headquarters in this embattled district are barely enough to keep the Taliban out. Perhaps more problematic is that the crumbling facade appears to be keeping the soldiers in.

Nolay Base takes direct fire almost every day from the Taliban. With more forces lost here than almost any other district in the country, the Afghan soldiers seldom leave the installation, and mostly refuse to conduct missions — too dangerous, they say. And when soldiers head out to go on brief home leaves, a growing number of them desert rather than return, their commanders say.

“It’s difficult to find local people who are against the Taliban,” said the executive officer of the brigade here, Col. Abdulhai Neshat. “This place is like a prison.”

In this corner of Helmand Province, widely agreed to be the most critical running battle in the country today, Afghan forces are in trouble. Though it does not reflect the broader security situation in Afghanistan, Sangin (pronounced SANG-in) offers a troubling portrait of life where the Taliban decides to make its mark and the Americans no longer fight, a situation that is likely to multiply as coalition forces completely withdraw next year.