Vice President Joe Biden says the U.S. is prepared to hold direct talks with Iran in the standoff over its nuclear ambitions — but only if the leadership in Tehran "is serious," The Associated Press reported.

Washington has indicated in the past that it's prepared to hold talk directly with Iran, and talks involving all five permanent members of the UN Security Council plus Germany have made little headway.

Asked at an international security conference when direct talks might be possible, Biden replied Saturday, Feb 2: "when the Iranian leadership, the supreme leader, is serious."

Biden says the offer stands "but it must be real and tangible and there has to be an agenda that they're prepared to speak to. We're not prepared to do it just for the exercise."