From Time Magazine:
Unless Iran responds positively to President Obama's offer of talks on its nuclear program by next month, it could face what Secretary of State Hillary Clinton calls "crippling sanctions." That was the message from Administration officials touring the Middle East in recent weeks. And it's backed by congressional moves to pass legislation aimed at choking off the gasoline imports on which Iran relies for almost a third of its consumption, by punishing third-country suppliers. It sounds impressive and, for an undiversified economy like Iran's, potentially calamitous. But a number of Iran analysts are skeptical that new sanctions will break the stalemate.
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My Comment: Sanctions have never worked in stopping the smuggling of technology, information, and equipment to blacklisted countries. In Iran's case, it's long border with Pakistan provides the conduit for any goods or tech to be easily smuggled into the country.