U.S. Secretary of State John Kerry has cancelled plans to return to the United States for an event honoring his late Senate colleague Edward Kennedy in order to remain at the ongoing Iran nuclear talks in Switzerland.

The State Department says Kerry had been looking forward to participating in the dedication of the Kennedy Institute in Boston with the family of the late Massachusetts Senator on Sunday and Monday but due to the ongoing negotiations he "regrets will not be able to share this special time with them in person." Kerry served in the Senate with Kennedy for nearly 25 years.

Kerry's decision to stay at the nuclear talks comes amid signs of the discord in the Iran negotiations ahead of a March 31 deadline for a preliminary deal.