Iran insists its nuclear work is peaceful and aimed at developing a new energy source.

Iranian worshippers shout anti-U.S. slogans during a Friday prayers ceremony in Tehran June 2, 2006. [Reuters]

Mottaki, Iran's foreign minister, welcomed the idea of direct talks but rebuffed the U.S. condition that Tehran must suspend uranium enrichment before talks can begin.

At the White House, President George W. Bush warned that the confrontation would go to the Security Council should Iran continue to enrich uranium.

"If they continue their obstinance, if they continue to say to the world, `We really don't care what your opinion is,' then the world is going to act in concert," Bush said.

Bush said he got a "positive response" in a telephone conversation Tuesday with Russian President Vladimir Putin, adding, "We expect Russia to participate in the United Nations Security Council. We'll see whether or not they agree to do that."

Bush also spoke about Iran on Thursday with Chinese President Hu Jintao. He revealed little about that conversation, saying, "They understood our strategy."

The shift in U.S. tactics was meant to offer the Iranians a last chance to avoid punishing sanctions and to let the United States assert that it was willing to exhaust every opportunity to resolve the Iranian impasse without force.