Perpetrators of the Sept. 11, 2001, terrorist attacks "still base their leadership" in the region, President Barack Obama said in Afghanistan on Sunday.

The U. S.-led military operation in Afghanistan is "absolutely essential to America's safety and security" because of the 2001 attacks, Obama, addressing about 2,000 U. S. service men and women and some coalition troops at Bagram Air Base, said.

He also said, "And this is the region where the perpetrators of that crime, al-Qaida, still base their leadership. Plots against our homeland, plots against our allies, plots against the Afghan and Pakistani people are taking place as we speak right here. And if this region slides backwards, if the Taliban retakes this country and al-Qaida can operate with impunity, then more American lives will be at stake."

Obama also said during a public appearance with Afghan President Hamid Karzai "there has been "progress with respect to the military campaign against extremism in the region." Obama met with Karzai after arriving at Bagram Air Base on a trip the White House did not publicize in advance.

He further said, "Many of the troops that I ordered to Afghanistan have begun to arrive, and more are on the way. And here in Afghanistan you've gone on the offensive. And the American people back home are noticing. We have seen a huge increase in support in -- stateside, because people understand the kinds of sacrifices that you guys are making, and the clarity of mission that you're bringing to bear." (With Inputs from Agencies)