US Secretary of State John Kerry is on his way to Geneva to join nuclear talks between six major powers and Iran, the US State Department said.

"After consulting with EU High Representative [Catherine] Ashton and the negotiating team on the ground, Secretary Kerry will travel to Geneva later today with the goal of continuing to help narrow the differences and move closer to an agreement," State Department spokeswoman Jen Psaki said.

Speaking to reporters earlier during her daily briefing – before Mr Kerry's travel was announced – Ms Psaki suggested that his going should not necessarily be taken as a sign that any deal with the Iranians was imminent.

"Even if the secretary travels, it is not a prediction of the outcome," she said earlier at her daily briefing.

"These negotiations are ongoing, there are tough issues on the table, that is what the negotiating team is working through."

Six major powers are seeking to negotiate an agreement with Iran in Geneva that would place some restraints on the Iranian nuclear program in exchange for easing sanctions against the Islamic republic.

The United States and some of its allies suspect that the Iranian nuclear program is designed to develop nuclear weapons, which the US regards as a threat to Israel and to other US allies in the Middle East.

Iran denies its program is to develop an atomic bomb, saying it is for civilian uses such as generating electricity.