OREANDA-NEWS. Diplomats from six global powers and Iran continue their negotiations over Tehran's nuclear program but have yet to reach a deal to swap oil sanctions relief for nuclear concessions.

The White House said today that negotiators in Vienna have closed some key issues. While calling that a "good sign," the US administration said "there continue to be some sticking points that remain unresolved."

The White House said that if the parties cannot conclude their negotiations today negotiators are likely to extend an interim agreement that imposes some limits on Iran's nuclear activities.

Iranian president Hassan Rohani's office raised expectations earlier today, when Rohani sent a tweet suggesting that the marathon negotiations had been successfully concluded.

"Iran deal is the victory of diplomacy & mutual respect over the outdated paradigm of exclusion & coercion. And this is a good beginning," the tweet read.

But that tweet quickly disappeared from Rohani's Twitter feed, replaced by a tweet that read: "If Iran deal, victory of diplomacy and mutual respect over outdated paradigm of exclusion and coercion. And this will be good beginning."

During the nuclear talks, Iran's oil exports have been limited to 1mn-1.1mn b/d, down from 2.5mn b/d before the sanctions were imposed. Iranian oil minister Bijan Namdar Zanganeh has said Iran will able to ramp up production quickly after a deal is announced. Iran produced 2.85mn b/d in June, tied with the UAE as Opec's third largest oil producer.

For President Barack Obama, an Iran nuclear agreement would constitute his signature foreign policy achievement, but any deal must survive a review by Congress. Senate majority leader Mitch McConnell, in a television appearance yesterday, said an agreement "is going to be a hard sell."

Under the Iran Nuclear Agreement Review Act, Congress would have 60 days after Obama sends an agreement up to Capitol Hill. If lawmakers do not like the agreement, they can vote to pass a resolution of disapproval, a development McConnell deems likely. Obama could then veto that legislation. That process could take up to 12 days.

And then lawmakers would have another 10 days to try to override a presidential veto, for a total of 82 days in all. Obama knows "that the resolution of disapproval is likely to be introduced, is very likely to pass and very likely to get over 60 votes," McConnell said. McConnell expects any decision will come down to whether Obama can hold the support of 34 senators to block a veto.

The length of time Congress would have to review an agreement doubled from 30 to 60 days because Obama could not present an agreement by 10 July. The White House has downplayed the significance of that change, since Congress will be away for a month-long August recess.