U.S. Secretary of State Condoleezza Rice says Iran must suspend uranium enrichment in a verifiable fashion before negotiations can begin on its nuclear program.
Ms. Rice made the remarks Monday during a trip to Canada.
Iran's chief nuclear negotiator, Ali Larijani, and European Union foreign policy chief Javier Solana met Saturday and Sunday in Vienna to discuss the nuclear issue.
Diplomats say Larijani offered to consider a temporary suspension of enrichment activities during negotiations, but Iran publicly denied making the proposal.
Earlier Monday, senior U.S. diplomat George Schulte welcomed progress at the talks between Solana and Larijani. However, he told reporters in Vienna the U.S. still intends to push for sanctions unless Iran suspends uranium enrichment.
Iran ignored an August 31 U.N. deadline to stop enriching uranium.
Also Monday in Vienna, the head of the U.N. nuclear agency, Mohamed El-Baradei, said the window of opportunity is shrinking to reach a settlement. He called for more negotiations.
The United States and other Western nations have accused Iran of enriching uranium for a secret nuclear weapons program. Tehran insists its nuclear activities are for peaceful, civilian purposes.
Some information for this report was provided by AP and Reuters.