WASHINGTON - The U.S. is paying six times as much to send war supplies to troops in Afghanistan through alternate routes after Pakistan's punitive decision in November to close border crossings to NATO convoys, the Associated Press has learned.

Islamabad shut down two key Pakistan border crossings after a U.S. airstrike killed two dozen Pakistani soldiers in late November, and it is unclear when the crossings might reopen.

Pentagon figures provided to the AP show it is now costing about $104 million per month to send the supplies through a longer northern route. That is $87 million more per month than when the cargo moved through Pakistan.

While U.S. officials have acknowledged that using alternate transportation routes for Afghan war supplies is more expensive and takes longer, the total costs had not been revealed until now. The Pentagon provided the cost figures to the AP on Thursday.

U.S. officials said Thursday the elevated costs are likely to continue for some time, as U.S.-Pakistan tensions remain high and Pakistan has not yet offered to restore the transport arrangement or to begin negotiations on the matter. Until the closure, the U.S. had relied on Pakistani routes to move about one-third of all war supplies for Afghanistan.

The U.S. has given Pakistan more than $20 billion in aid since 9/11, including civilian and military assistance. But over the past year, relations with Islamabad have been strained by a series of incidents, including the U.S. assault in Pakistan last May that killed Osama bin Laden.

Pakistani leaders have also complained about repeated U.S. drone strikes into their country. The strikes, largely by the CIA, target militants hiding along Pakistan's border who launch attacks against NATO troops in Af-ghanistan.

The final straw, however, was the Nov. 26 cross-border attack that hit two Pakistani border posts, enraging the Pakistani government and further eroding already shaky relations.

Over the past year or so, the U.S. military has been shrinking its reliance on the Pakistani routes.

Suicide bombers kill 19

Meanwhile, two attacks in southern Afghanistan have left at least 19 people dead over the past two days, Afghan officials said. The attacks come at a critical moment in peace talks between the United States and the Taliban.

On Thursday morning, a suicide bomber killed six civilians near the entrance to a NATO airfield in Kandahar, said a provincial spokesman. Two of the dead were children. The Taliban asserted responsibility.

On Wednesday, 13 people were killed and 20 wounded when a suicide bomber attacked a bazaar in Helmand province.