"I wish they were not pursuing any nuclear program," he added. "But the fact of the matter is whether we argue about whether they should or shouldn't, they have it. The centrifuges are spinning. They're producing the material. And the policy so far has not caused them to stop doing that."
Powell was supportive of President Obama's Afghanistan strategy, but said that U.S. forces eventually must leave.
"Ultimately," Powell said, "the United States Army and Marine Corps cannot remain in Afghanistan forever as police forces."
Powell said there are challenging questions facing the president on Afghanistan.
"We have had this additional input of 68,000 soldiers, bringing it to over 100,000 soldiers," he said. "We have done what we said we were going to do. Have the Afghans done what they must do -- build an army that is capable, an army that is connected to the central government, an army that the people believe in?"
He cited other open questions.
"Do we have a police force that is not corrupt? And do we have a government in Kabul that is really reaching out and connecting the people together into some kind of political system that people believe in?" Powell asked.
In the end though, Afghanistan's fate will be decided by Afghans, the former secretary of state said.
"Ultimately," he said, "we can do just so much, but to win this conflict and to create the kind of Afghanistan that we all want to see, it ultimately is going to be in the hands of the Afghans."