"If we are able to verify that in fact they are not developing weapons systems, then there's a deal to be had," Obama told CBS News in an interview aired Sunday on "Face the Nation."

"But that's going to require them to accept the kind of verification and constraints on their program that so far, at least, they have not been willing to say yes to," he said.

His comment comes as the talks with Iran enter a key stretch, with an international group of negotiators aims for an outline of an agreement by the end of March -- with a full dead to follow by the end of June.

Israeli Prime Minister Benjamin Netanyahu warned in a high-profile speech to Congress last week that Iran shouldn't be trusted -- and that the country could grow its number of centrifuges used to enrich uranium after the deal ends.

Also key to the deal is Iran's "breakout period" -- the length of time it would take the country to amass enough enriched uranium to build a nuclear weapon, rather than just nuclear power for civil use.

"If there's no deal, then we walk away," Obama told CBS News. "If we cannot verify that they are not going to obtain a nuclear weapon, that there's a breakout period so that even if they cheated we would be able to have enough time to take action, if we don't have that kind of deal, then we're not going to take it."

(CNN)