Washington ? The chairman of the military’s Joint Chiefs of Staff says the U.S. is trying to be patient with Pakistan, which has closed critical supply routes in protest over a U.S. airstrike two weeks ago that killed 24 Pakistani troops.

But Gen. Martin Dempsey says transporting fuel and other supplies to troops in Afghanistan through alternate northern routes will be more expensive and time consuming. Pentagon officials on Friday said they don’t yet know how much more it will cost.

Dempsey says he’s more concerned about the impact of the airstrike on America’s long-term relationship with Pakistan. He says both sides are trying to be patient and work through the problems.

Dempsey was speaking at a forum hosted by the Washington-based Atlantic Council.