Defense Secretary Robert Gates said on Sunday that economic sanctions would be more effective than diplomatic overtures in bringing Iran to the negotiating table over its nuclear program.

"Perhaps if there is enough economic pressure placed on Iran, diplomacy can provide them an open door through which they can walk if they choose to change their policies," Gates said on Fox News Sunday.

"I think the two go hand in hand, but I think what gets them to the table is economic sanctions," he said, commenting on diplomatic efforts to neutralize the nuclear plans of Iran and North Korean.

Gates clarified the Pentagon''s view that Iran may have enough low-enriched uranium from centrifuges at the Natanz nuclear facility, but it does not have the capability to enrich the material further to weapons grade.

The U.S. government suspected Iran could be "clandestinely" building an enrichment capability, he said, but added:

"We do not believe they are doing enriching beyond a low level at Natanz, and the (International Atomic Energy Agency) is in there, so we will know if they tried to do that."

In separate comments on Sunday, the chief of the U.S. Central Command, Gen. David Petraeus, said Iran and the United States shared common goals in stabilizing Afghanistan.