The cost of supplying the U.S. war effort in Afghanistan has soared since Pakistan closed its borders to coalition forces.

Pakistan is supposed to be a U.S. ally in the war on terror; however, it refuses to let NATO supply convoys pass through the country.

The country's military closed its two main supply routes after a U.S. air strike accidentally killed two dozen Pakistani soldiers last November.

Pentagon officials said using a northern route to supply the war is costing the U.S. $104 million a month. That's an increase of $87 million from when supplies were sent through Pakistan.

U.S. officials said it's not clear when Pakistan will reopen its borders to coalition forces.

Until the closure, the U.S. moved up to one-third of its supplies along the Pakistani supply routes to Afghanistan.