Petraeus, the head of U.S. Central Command, said "tough fighting" is taking place in southern Afghanistan.
"It's hard, but we're there for a very, very important reason," Petraeus told NBC's "Meet the Press." "We're in Afghanistan to ensure that it cannot once again be a sanctuary for the kind of attacks that were carried out on 9/11."
Petraeus said about 5,400 of the 30,000 additional forces President Obama announced in December would deploy now are on the ground. He said while the fighting is tough, it has already started producing some initial captures of Afghan shadow governors, Taliban shadow governors and other high-value targets.
In executing the "clear, hold, build" strategy, Petraeus said that the Afghan war isn't just aimed at killing and capturing Taliban and Al Qaeda elements, but also training about 100,000 Afghan Security Forces and reintegrating some low-level fighters who are willing to reconcile.
Meanwhile, the general said that while Al Qaeda is diminished, it is still interested in attacking the United States.
"This is an enemy that is looking for any opportunity to attack our partners and indeed, our homeland. And we have to keep that in mind. There's no question about its desire to continue to attack our country and our allies," he said.
"This is Iraqracy at work, not necessarily western democracy. But, this is a government that is representative of all of the people. It is responsive to the people," he said, adding that "there is a fierce campaign" and "high political drama" going on ahead of the March 7 provincial election that will choose the Iraqi parliament and council of representatives.
Speaking on CBS' "Face the Nation," former Secretary of State Colin Powell defended the Bush administration's decision to go to war in Iraq, saying the United States gave the Iraqi people the chance for a "new life" in which people there "have their own destiny in their own hands."
Powell added that he doesn't think the United States handled the aftermath of the fall of Baghdad well, but "that's now history."
Fox News' Molly Henneberg and Nicole Collins contributed to this report.