Speaking in New York on September 19, the same day the UN opened its General Assembly, Burns said the United States will pursue UN Security Council sanctions against Iran if the EU's talks fail to persuade Iran to verifiably halt uranium-enrichment activities.
Burns said a deadline for the Iran-EU talks to achieve results had been set by the six powers -- permanent Security Council members China, Russia, France, the United Kingdom, and the United States -- plus Germany.
He declined to give a date for that agreed deadline.
China and Russia have consistently signaled their unwillingness to impose sanctions on Iran, and French statements this week have urged further diplomatic efforts to resolve the nuclear stalemate.
Iran spurned a Security Council deadline of August 31 to suspend its enrichment and has insisted on its right to a nuclear program under the Nuclear Non-Proliferation Agreement, to which it is a signatory.
The United States has been vocal in its accusation that Iran's nuclear program includes a clandestine weapons-development effort, a charge that Tehran has consistently rejected.
The UN nuclear watchdog, the International Atomic Energy Agency (IAEA), has criticized Iranian officials for a lack of disclosure and said Tehran has not provided sufficient evidence to indicate its nuclear program is strictly civilian.