American commanders in Afghanistan are sending more U.S. troops to Helmand province in response to a surge in violence as Taliban insurgents seize new ground at the center of the region's lucrative opium industry, defense officials said.

The additional troops — U.S. officials won't reveal the precise number — will include some ground-level combat advisers working alongside Afghan special operations forces as well as additional U.S. Army infantry soldiers providing enhanced force protection for the American advisers, officials said.

"We are increasing our number of advisers in Helmand, and the force protection that will be there for those troops will be what is appropriate given the number of troops we have down there," Brig. Gen. Wilson Shoffner, a U.S. military spokesman in Afghanistan, told reporters Thursday.

Reports from U.S. and Afghan officials suggest the number of additional troops could be more than 500. Shoffner declined to provide specific numbers for the size of the U.S. force in Helmand. The size of the total U.S. force in Afghanistan, around 10,000, will not change, he said.

It marks one of the largest regional deployments for U.S. troops in Afghanistan since the U.S. combat mission there ended in 2014. The uptick in forces for Helmand comes as soldiers from 2nd Battalion, 87th Infantry Regiment, of Fort Drum, New York, are preparing to deploy and replace a unit of U.S. troops that has been in Helmand for months.

The new operation comes after the Taliban launched a major offensive in Helmand several months ago, targeting it in part for control of the opium trade. Taliban militants have recently threatened to seize control of major cities, including Sangin and Marjah near the provincial capital of Lashkar Gah.

The Afghan army unit there, the 215th Corps, has performed poorly. Top Afghan officials recently fired its commander amid reports of incompetence and corruption.

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Shoffner noted that the current mission in Helmand does not involve direct combat with Taliban fighters.

"With the Afghan special forces, we're conducting the train-advise-and-assist down to the tactical level," the general said.

"What we're not doing is putting the troops in the train-advise-and-assist role on the objective. So, those forces … will participate in the planning. They'll participate in the coordination for air, for intelligence. They may participate in the coordination for transportation. … But when the operation actually occurs, those trainers are breaking off and they'll go to an overwatch position or they'll go to a command-and-control location," Shoffner said.

"So they're not actually on the objective when the operation is occurring," he said.