Key Issues Unresolved as Iran Nuclear Talks Continue Past Deadline

— -- Foreign negotiators, working beyond a Tuesday deadline, are optimistic that an agreement can be drafted on a nuclear accord with Iran -- with a focus on narrowing down differences between the parties.

A joint statement of progress is expected later today.

British Foreign Secretary Philip Hammond, speaking to reporters, said “a broad framework of understanding” exists, but that some issues still need to be worked out. Germany’s foreign office shared similar sentiments, writing in a statement, “Progress is visible. Nothing is agreed but if there is good will on all sides an agreement is possible."

A deadline for the agreement had been set for March 31. While the deadline has passed, Iran’s foreign minister, speaking Tuesday, said the negotiations have been productive.

"We've accomplished quite a bit, but people needed to get some rest and start over early in the morning," Iranian Foreign Minister Mohammad Javad Zarif said. "And I hope we can finalize the work on Wednesday -- and hopefully begin the process of drafting."

The State Department had said earlier Tuesday that despite progress, obstacles still remain.

"We've made enough progress in the last days to merit staying until Wednesday," State Department spokeswoman Marie Harf said in a statement to reporters in Lausanne, Switzerland, where the talks are being held. "There are several difficult issues still remaining."

Sticking points during these talks included disagreements on how many centrifuges -- which are used to enrich nuclear fuel -- might remain online at Iran's deep-buried Fordo nuclear reactor, whether or not Iran will be allowed to continue nuclear research and development for scientific purposes, and what to do with the stockpile of enriched uranium it already owns.

Negotiators on all sides have been working towards this deadline since November 2013. That's when Iran and the so-called P5 +1 (U.S., U.K., France, Russia and China, plus Germany) agreed on a Joint Plan of Action (JPA), an interim agreement that paved the way for talks by temporarily halting Iran's nuclear enrichment program and subjecting it to daily inspections in exchange for the loosening of some economic sanctions.

"If we are making progress toward the finish line, then we should keep going," White House spokesman Josh Earnest said Tuesday, but he added that if talks fail, then the U.S. would be forced to "consider some other alternatives.”