"I think that the president's opposition to a bill that would impose additional sanctions now is absolutely right," Gates said yesterday at an event highlighting his newly released memoir.
"To vote additional sanctions today would be I think a deal-killer," said Gates, who served as defence secretary under President Barack Obama and his predecessor, George W Bush.
The Obama administration has lobbied against a push by some members of Congress to introduce additional economic sanctions over Iran's nuclear program, saying it would undermine recent diplomatic progress after Tehran agreed to a six-month interim accord.
"I think we have succeeded to the extent that we now have the Iranians at the table."
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He pointed to the clear effect of economic pressure on the Islamic republic.
The former CIA director did say he favoured a mechanism - either through legislation or a "formal commitment" - that if talks fail, Iran would face even more drastic economic penalties than those in place before the interim deal.
Gates, a Republican with a reputation as a hard-nosed pragmatist when it comes to foreign policy, reiterated his view that bombing Iran's nuclear facilities would not eliminate the program and merely set it back by a few years.
"I think it's a steep hill because the only acceptable agreement for the longer term is one that rolls back the Iranian program from allowing Iran to be a nuclear weapons threshold state," he said.
And an agreement would have to provide "intrusive enough inspections that ensures that if they decide to violate the agreement, we have ample time to react militarily or in other ways."