While both the United States and the EU hope to resolve the issue in a diplomatic way, they have also reached consensus that the next step against Iran must involve sanctions, said Ambassador Gregory Schulte.

The United States is "waiting for the new explanation from Iran," Schulte told the Austria News Agency. If Iran would not stop its "discomforting activities," the UN Security Council should discuss the sanctions against Iran, he said.

Schulte stressed the common stand with the EU ahead of Wednesday's talks between EU foreign policy chief Javier Solana and top Iranian nuclear negotiator Ali Larijani. The talks are considered by many a final chance to compromise on enrichment, which Tehran has vowed not to give up.

Observers see the Solana-Larijani meeting as the prelude to Thursday's conference of the five permanent members of the UN Security Council -- the United States, Russia, China, France, Britain -- plus Germany.

The flurry of diplomacy followed Tehran's rejection of UN resolution 1696 which had called on Iran to suspend its uranium enrichment program by Aug. 31.

On their informal conference on Saturday, the EU foreign ministers decided to maintain the serious talks with Tehran in efforts to solve Iran's nuclear issue through diplomacy.