Turkey, which has agreed to join the U.S.-led airstrikes against the Islamic State group, needs to do more to fight the militants and control its own borders, U.S. Defense Secretary Ash Carter said Thursday.
Turkey has focused its fighting in major Kurdish areas.
Islamic State fighters and equipment have been able to cross into Iraq and Syria from Turkey.
"We need them also as a neighbor to this conflict zone, as a longtime NATO ally and a responsible member of the anti-ISIL coalition to control ... the long border that they have with both Syria and Iraq, more than it has been controlled over the last year," Carter said.
The secretary said he does not think the Turks are "dragging their feet," but said their increased participation, including joining the airstrikes, is "overdue."
"It's a year into the campaign, but they're indicating some considerable effort now, including allowing us to use their airfields. That's important, but not enough."
Carter said President Barack Obama has also been part of the active discussions with Turkey to get more involved.
Turkey agreed last month to allow U.S. jets attacking Islamic State to use Incirlik Air Base, but it has focused its increased military participation in the region on its own long-running fight against Kurdish guerrillas.
U.S. intelligence says even after a year of the U.S. bombing campaign and some success on the ground by Iraqi forces, the Islamic State is no weaker today than last September.
Carter refused Thursday to characterize the situation as a "stalemate." He said he is confident that the Islamic State will be defeated and that the U.S. is using the right strategy.But he said the fight is complicated and requires hard work.