Secretary of State John F. Kerry said early Sunday he would be unable to attend the Monday dedication of an institute honoring the late Sen. Edward M. Kennedy, an acknowledgement that negotiations seeking a deal to curb Iran’s nuclear program would not be finished Sunday, as had been hoped.

In a statement from this city, where negotiations have been underway since Thursday, a spokeswoman for Kerry said he regrets that he will not be able to attend the dedication with the family of the Massachusetts Democrat “given the ongoing nuclear negotiations.”

Both U.S. and Iranians officials were hoping to finish a preliminary agreement on the nuclear program Sunday, and to fly home at the end of the day. But Iran has not met the demands of the U.S. and five other world powers on several remaining issues. It is now uncertain if the two sides will reach a deal by the Tuesday deadline.

The two sides are seeking a deal that would ease sanctions on Iran if it accepts curbs aimed at keeping it from obtaining a nuclear weapon.

“Secretary Kerry was very much looking forward to being a part of the Edward M. Kennedy Institute's dedication in Boston this week, and to honoring the work of his friend's life, and [the Senate], where they served side by side for nearly 25 years, with the Kennedy family and Sen.  Kennedy's friends,” spokeswoman Marie Harf said in the statement.

The foreign ministers for the world powers have been arriving this weekend in hopes of smoothing remaining disagreements and giving their countries’ blessing to the deal.

But as often happens in such negotiations, the closing days have been contentious. Both sides are under intense pressure to get the best possible terms, because they face powerful resistance to the agreement in their home countries.

By Los Angeles Times