(JTA) – The negotiations in Switzerland over a framework deal with Tehran are being extended by a day.

A spokesman for the U.S. State Department, Marie Harf, told reporters on Tuesday that the talks would be extended past that day’s deadline for a framework agreement. The deadline for a comprehensive deal is June.

“‎We’ve made enough progress in the last days to merit staying until Wednesday,” Harf told reporters. “There are several difficult issues still remaining.”

There reportedly are a few sticking points to a deal, including the pace of lifting the sanctions on Iran, whether sanctions automatically will return if Iran violates the deal, whether Iran ships its nuclear fuel for processing outside the country, what to do with Iran’s existing stockpile of fissile material, and the degree to which Iran must open up its nuclear facilities to international inspectors.

The United States is leading the talks between Iran and six world powers. Joining the U.S. are the other four permanent members of the U.N. Security — Russia, China, Britain and France — plus Germany.

The March 31 deadline for a framework agreement is somewhat arbitrary. It was imposed about three months ago after the two sides decided to extend the overall negotiations to June 15. Iran and the world powers, known as the P5+1, had entered into an interim agreement on Nov. 24, 2013, with Iran agreeing to temporarily freeze some elements of its nuclear program in exchange for a temporary easing of certain sanctions while the two sides negotiated a final deal.

That six-month agreement took effect on Jan. 20, 2014. In July 2014, the two sides agreed to a four-month extension, and last November the deadline was extended again, to June 15, 2015. Shortly afterward, the goal was established to reach a high-level political agreement by March 31, and all technical issues by mid-June.