The Bush administration is trying to rally other nations to agree to impose U.N. sanctions on Iran to force it to negotiate an end to its nuclear programs.
Britain, France and Germany, negotiating for the European Union with U.S. support, has offered Iran economic incentives to stop converting uranium into fuel that could be used for nuclear weapons.
The United States has offered Iran spare parts for commercial aircraft and help in becoming a member of the World Trade Organization.
With the talks stalemated, however, the U.S. administration clearly is losing patience.
Iran's top nuclear negotiator, Ali Larijani, said Wednesday on a trip to India that Iran wants to cooperate in a serious way with the IAEA.
The Bush administration was not impressed.
"It sounds like a lot more words that are not backed by any actions," Sean McCormack, the State Department spokesman, said.
"What Iran needs to do is to re-engage with the EU-3 in serious, constructive negotiations," he said. "And we would encourage them to take the deal that is on the table now. It's a good deal."
The administration evidently has won over President Jacques Chirac of France to a hard line.
In an ultimatum issued Monday, Chirac warned Iran it would face censure by the U.N. Security Council if it did not reinstate a freeze on sensitive nuclear activities under an accord reached in Paris in November.
"The use of civilian nuclear energy, which is perfectly legitimate, must not serve as a pretext for pursuing activities that could actually be aimed at building up a military nuclear arsenal," he said.
Burns said he expected the governors of the IAEA, meeting two weeks from now, to "exercise their responsibility" and send the dispute to the Security Council.
And there, Burns said, "it is up to the international community to find a way to pressure Iran to go back to a position of negotiations and to suspend its nuclear activities."
"It is a very serious question, which deserves a serious response by the international community in the month of September," Burns said.
While not specifying whether the administration wants censure of Iran and economic and political penalties imposed, Burns said, "There has to be a graduated series of steps to bring Iran back to a position of negotiations and suspension of its nuclear activities.", AP reported.