"Iran has a choice: to comply with its international obligations and that would mean not only offering inspections (of its nuclear facilities) but ending its activities absent the kind of monitoring and supervision that would guarantee that what they are doing is solely for peaceful purposes," she told reporters.
"The alternative track," she added, was "greater isolation and international pressure."
Clinton said she would not prejudge the outcome of crunch talks in Geneva Thursday between top Iranian nuclear negotiator Saeed Jalili and senior officials from Britain, China, France, Germany, Russia and the United States.
She spoke after chairing a UN Security Council meeting on sexual violence against women in armed conflict.
The 15-member Council has imposed three sets of sanctions against Iran over its refusal to freeze its uranium enrichment activities which the West and Israel sees as a cover to acquire nuclear weapons.
The United States and its allies also want Iran to provide UN inspectors immediate access to a newly disclosed second uranium enrichment plant, which has raised suspicions about the true nature of its nuclear program.
The head of the UN nuclear watchdog, Mohamed ElBaradei, said that Iran was "on the wrong side of the law" by not declaring its new enrichment plant before last week.
Jalili meanwhile said Wednesday that he was heading for the talks with a "positive approach" while atomic energy chief Ali Akbar Salehi said Iran was ready to discuss concerns about its new enrichment plant.
