In addition to longer-term U.N. and other sanctions, Tehran is now being squeezed by the widening international embargo on its oil sales, which make up more than 90 percent of its foreign currency earnings.

Sanctions levied by the U.S. have already cut exports of Iranian crude from about 2.5 million barrels a day last year to between 1.2 and 1.8 million barrels now, according to estimates by U.S. officials. A European Union embargo on Iranian crude that starts July 1 will tighten the squeeze.

Comments by Ali Bagheri, the No. 2 on the Iranian delegation, reflected the gap between the two sides' priorities.

"We elaborated in detail ... the illegality of referring Iran's nuclear issue to the U.N. Security Council and issuance of U.N. Security Council resolutions," he told reporters, referring to Security Council demands — enforced by sanctions — that Iran stop enriching.