Panetta also touched on several other key security issues in the wide-ranging interview.
He said there are "at most... 50 to 100" members of al-Qaeda in Afghanistan, and that the bulk of the organisation is based across the border in Pakistan. US intelligence officials estimate al-Qaeda has less than 300 active members worldwide.
Panetta also defended US policy in Pakistan, saying that everything the US does there is "compliant with US and international law". The CIA runs the US programme of aerial drone strikes in Pakistan, though it does not publicly admit its role.
The CIA director also said the Iranian government has the capacity to produce a nuclear weapon within two years, though he stopped short of saying Iran had decided to pursue such a policy. Iran insists its nuclear programme is for peaceful purposes.