Story highlights U.S. cites risk to drivers and contractors along route to Pakistan

The United States faces continuing protests over drone strikes

About 33,000 tons of U.S. cargo shipped out of Afghanistan each month

The U.S. military, facing continuing protests over drone strikes, has halted military cargo shipments from Afghanistan, citing a potential risk to drivers and contractors along the route once it enters Pakistan.

"We are aware protests have affected one of the primary commercial transit routes between Pakistan and Afghanistan. We have voluntarily halted U.S. shipments," Defense Department spokesman Mark Wright said.

Halted operations through the Torkham Gate border crossing impacts more than half of all military shipments out of the war zone each month as American involvement in the war winds down.

On average, the United States ships about 33,000 tons of cargo out of Afghanistan each month.

The action was taken to stop shipments along the route from the border crossing to Karachi "to ensure the safety of the drivers contracted to move our equipment. We anticipate that we will be able to resume our shipments through this route in the near future," Wright said.

If the crossing does not re-open, shipments out of Afghanistan could be made by air, or longer land routes to the north, but both would be more costly in the long run. There is no indication what specific cost would be involved or how long the stoppage could last.

The decision also comes as the United States is trying to get Afghanistan to sign an agreement to keep some U.S. troops in the country after 2014. But the majority of the gear for the 47,000 troops still in Afghanistan will have to be brought out.