After days of saying Iranian nuclear talks can go either way, U.S. Secretary of State John Kerry is expressing optimism that a deal can be reached.

Kerry says he is "hopeful" after his last meeting with Iranian Foreign Minister Mohammad Javad Zarif. He says a "few tough things" remain in the way of agreement but "we're getting to some real decisions."

Kerry spoke Sunday, with less than two days to go to Monday's target date for a pact meant to impose long-term verifiable limits on nuclear programs that Tehran could modify to produce weapons. Iran would get tens of billions of dollars in sanctions relief in return.

The talks are now in their 16th day and have been extended three times since the first deadline of March 31 was missed.