Last Updated Jun 27, 2015 7:55 PM EDT
VIENNA -- Secretary of State John Kerry is under pressure to deliver President Obama's chief foreign policy goal - a nuclear accord with Iran. Kerry and his Iranian counterpart have until Tuesday to finalize an agreement.
Iran's supreme leader made that job more difficult this week, publicly staking out several hard lines. Ayatollah Ali Khamenei said nuclear inspectors would not be allowed to inspect military sites, a key U.S. demand.
He also wants all financial sanctions on Iran to be lifted immediately, not gradually as the U.S. has proposed.
There's pressure at home, too. Several former Obama aides warned in a recent letter that the emerging deal "may fall short of meeting the administration's own standard of a 'good' agreement."
James Jeffrey, the president's former ambassador to Iraq, signed that letter.
"We are worried that the administration is going to do a rush to signature and essentially cave to the supreme leader's most recent and absurd red lines," Jeffrey told CBS News.
Ali Rezaian's stake in a diplomatic breakthrough is personal. His brother, Washington Post Reporter Jason Rezaian, is in a Tehran prison on charges of espionage.
Desperate for help, Rezaian came to Vienna to lobby for Jason's release.
"I would say that it's clear that the evidence against him just isn't there; he's been locked up for 11 months now," he told CBS News. "They should look at what they're doing and that they're holding an innocent man, and it's inhumane, it's illegal, and it needs to end."
But a breakthrough is nowhere in sight.
Negotiators tell CBS News the talks have gotten extremely difficult as they try to draft the fine print of a deal that could define Mr. Obama's foreign policy legacy.