Last Updated Mar 30, 2015 7:05 PM EDT
LAUSANNE, Switzerland -- Negotiations over Iran's nuclear program have been extended until Wednesday, the State Department said Tuesday.
Secretary Kerry made an eleventh hour decision to stay in Switzerland because there had been enough progress to merit at least another day of talks. Still, several difficult issues are holding up an agreement. The two sides are still arguing over how much nuclear fuel Iran will be allowed to produce in the future, as well as how to verify the fuel is being used only for peaceful purposes.
Another challenge the parties are struggling with is whether and when to lift the U.N. sanctions that have cut Iran off from global markets.
At home, Secretary Kerry will also have to deal with the U.S. Congress, and that could prove even more difficult than negotiating with the Iranians. He is faced with having to persuade skeptical Republicans -- and some Democrats -- that this deal will prevent Iran from building an atomic bomb, and as a result there is no need for any new sanctions.
The Iranians, on the other hand, will need to convince hardliners at home that they gained more than they gave up. But should they succeed in promoting that message, it could make the deal even less palatable for Congress.
Earlier Tuesday, State Department acting Spokesperson Marie Harf told reporters, "We've made enough progress in the last days to merit staying until Wednesday. There are several difficult issues still remaining."
Russian Foreign Minister Sergey Lavrov was on his way back to Lausanne from Russia, indicating an end to the talks was near. He had left Lausanne on Monday but said he would return if a deal were imminent.
The final deadline for an agreement is late June, but the parties hope to come up with a framework for Iran's nuclear program now.