Turkey could do more in the fight against Islamic State (ISIS) militants, US Secretary of Defense Ashton Carter said on Friday."Turkey is a longtime friend of ours. It's a NATO ally. We're strongly in support of it. We stand with it in terms of defense of its own territory," Carter said at the World Economic Forum in Davos."But the reality is it shares a big border with Iraq and Syria, which border has been porous to foreign fighters going in both directions and I think the Turks could do more," Carter added."I think the Turks can do more to fight ISIL. They are helping us fight ISIL by for example hosting our aircraft in Turkey, I'm grateful for that. But I think they can do more."