Pentagon says halts ground shipments out of Afghanistan via Pakistan WASHINGTON (Reuters) - The U.S. military has halted ground shipments of cargo leaving Afghanistan via its key Pakistan supply route to ensure the safety of drivers following protests in Pakistan over American drone strikes, a Pentagon spokesman said on Tuesday. The affected route, which runs from Torkham Gate at the Afghanistan-Pakistan border to the Pakistani port city of Karachi, has been crucial for the United States as it winds down its combat mission in landlocked Afghanistan and moves equipment out of the country. The route accounts for the vast majority of ground traffic of U.S. military cargo through Pakistan and has been targeted by protesters in Pakistan angered by U.S. drone strikes. "We are aware protests have affected one of the primary commercial transit routes between Pakistan and Afghanistan," Pentagon spokesman Mark Wright told Reuters. "We have voluntarily halted U.S. shipments of retrograde cargo ... to ensure the safety of the drivers contracted to move our equipment," he added, referring to shipments going out of Afghanistan. The U.S. decision to temporary suspend its use of the route is another headache for military planners just as Afghan President Hamid Karzai throws into doubt American plans to keep some forces in Afghanistan after NATO's combat mission ends next year. Karzai has so far refused to sign a bilateral security pact the United States and NATO say are crucial for some international forces to stay to advise and assist Afghans. Wright said the U.S. military expected it could resume its retrograde shipments through the Pakistani route in the near future. He also pointed out that the United States has other options to move equipment out of the country. Still, other options are far more costly, including the shipments via the so-called Northern Distribution Network, a complex web of transit routes through Russia and Central Asia. That route is key in bringing supplies into Afghanistan. The United States also flies equipment out of Afghanistan in jets, including munitions and weapons. The U.S. military had to rely on those alternatives, however, when Pakistan closed down the routes to protest a NATO cross-border killing of Pakistani soldiers in 2011. Although there is another ground supply route through Pakistan, closure of the main route essentially shuts off retrograde shipments, one U.S. official said, speaking on condition of anonymity. The United States still has about 46,000 troops in Afghanistan, a figure set to fall to 34,000 by early next year. As NATO winds down its operations, it is handing responsibility for fighting Taliban insurgents to the Afghans, before most foreign combat forces pull out by the end of 2014. U.S. and NATO officials have warned that if Karzai does not sign the security deal with the United States promptly, both Washington and the alliance would have to withdraw all troops from Afghanistan by the end of 2014. NATO officials have also warned that, if all foreign troops left, it could put at risk billions of dollars in foreign aid because donors would be reluctant to contribute to funding Afghan security forces if there were no foreign troops on the ground to see how the money was spent. Reporting by Phil Stewart; Editing by Jackie Frank and Lisa Shumaker