Rubio told reporters in New Delhi that the US would give diplomacy every chance to succeed before exploring "alternatives", after President Donald Trump said on Sunday he had told his representatives not to rush into any Iran deal.
There was no immediate response from Iran's government. But the Tasnim news agency, linked to Iran's Revolutionary Guards, said the US was still obstructing parts of a potential deal, including Tehran's demand for the release of frozen funds.
The two sides remain at odds on several difficult issues, such as Iran's nuclear ambitions, Israel's conflict with Hezbollah militia in Lebanon, and Tehran's demands for the lifting of sanctions and the release of tens of billions of dollars of Iranian oil revenues frozen in foreign banks.
