Just months after pulling out of a remote slice of eastern Afghanistan dubbed the "Valley of Death," U.S. troops are back reinforcing their once-abandoned bases in the area — a hotbed of the insurgency and a dangerous second front in the decade-old war.

Stationing U.S. troops again in the isolated, sparsely populated Pech Valley will boost the coalition's presence and firepower in the area near the Pakistan border just as the focus of the war shifts back to that region where infiltrating insurgents closest to al-Qaida and other militants hold sway.

"The decision to send U.S. forces back to the Pech may also reflect a recognition that insurgent safe havens can cause us more harm than had been anticipated when we withdrew U.S. forces," said Mark Moyar, research director of the U.S.-based counterinsurgency consultancy Orbis Operations.

"Insurgencies thrive on such safe havens and use them to stage operations elsewhere," he said.

The U.S. military downplayed the decision to station troops again in Pech. The coalition, along with the Afghan National Army, always maintained a presence in the region, said Lt. Col. Chad Carroll, a spokesman for the coalition's eastern command.

"It's just a matter of where they laid their heads at night," he said.