Chuck Hagel expresses regret over Taliban joke

US Defence Secretary Chuck Hagel has expressed regret to an Indian-born college professor for jokingly asking, "you're not a member of the Taliban, are you?" seconds before the professor rose to ask a question.

Hagel's spokesman said the joke was not directed at anyone in particular, and the defence secretary called the professor, Robin Gandhi, to tell him as much hours after the event at the University of Nebraska, where Hagel gave a speech and took questions from the audience.

Hagel "expressed regret for any trouble that this caused the professor," spokesman George Little told reporters.

"They had a very good discussion and (Hagel) wanted to leave no impression that this joke was directed at anyone in particular, including the professor," Little said.

He added that the defence secretary a little earlier in the programme had answered a question about the Taliban, the Afghan insurgent group.

Gandhi said in a statement that he was honoured to hear Hagel's speech and enjoyed the secretary's answer to his question about cyber weapons.

"Before I rose to ask a question, there was apparently some confusion that did not involve me," Gandhi said, suggesting he too did not believe Hagel's joke was addressed at him.