EU foreign affairs head Catherine Ashton, who leads talks with Tehran on its disputed nuclear program, on Tuesday called on Iran's new president to agree a fresh round of negotiations as soon as possible.

Ashton in a letter offered her congratulations on President Hasan Rowhani's inauguration and said he had won "a strong mandate to engage in dialogue and cooperation with the international community to seek a swift resolution to its serious concerns about Iran's nuclear activities.

"I write to tell you that, together with the (P5+1), I stand ready to continue talks to find a resolution as quickly as possible," a statement quoted her as saying.

"I hope that we can schedule meaningful talks with your negotiating team as soon as practicable," she said.