On Wednesday, Under Secretary of State for Political Affairs Nicholas Burns testified before House Committee on Foreign Affairs on US policy toward Iran. His submitted testimony essentially reiterates the administration's commitment to confronting Iran's nuclear ambitions through diplomacy at the Security Council. But according to an eyewitness to the hearings, some members of Congress expressed skepticism about this route, particularly when it came to the utility of the Security Council sanctions imposed on Iran last December.

To this, the eyewitness reports that Burns responded:

"Iran is in a position where it is one now of only 11 countries in the entire United Nations -- out of 192 -- that are under sanction. And it's been that spotlight -- and here I would just have to disagree, very respectfully, with some of the comments made -- it's those sanctions that have worried the Iranian government...

So I would argue to you that this diplomatic process of trying to use the United Nations and trying to use a multilateral framework for negotiations is the right path for the United States...When the Security Council resolution passed on December 23rd, I will tell you that I felt perhaps it wasn't strong enough too...And we have been pleasantly surprised to see the impact it's had inside Iran. I think the Iranians are less concerned with the specific aspects of those sanctions than they are with the isolation that it's brought them and the international condemnation that it's brought them. And I think they were surprised that Russia and China joined us."

With this comment, Burns adds himself to the growing, but under acknowledged, number of commentators and policy makers who believe that the UN sanctions regime is starting to show its intended effect inside Iran.

True, the sanctions are not as tough as they could be. Just this week the Security Council began a new round of negotiations discussing how to strengthen the sanctions package, including expanding the number of individuals slapped with a travel ban and asset freeze. Still, as Burns, and others like the Hoover Institution's Abbas Milani have argued, it's not the actual sanctions package so much as the prospect of further international isolation that has Tehran worried.