The official IRNA news agency said Catherine Ashton arrived in Tehran today for talks with Iranian leaders, including President Hassan Rouhani.
Ashton leads the six-nation group -- the US, Britain, France, Russia, China and Germany -- in talks with Iran over Tehran's nuclear program. Iranian media say the visit signals the normalisation of Iran's relations with Europe after eight years of tension under Rouhani's predecessor, President Mahmoud Ahmadinejad.
Iran struck an initial deal with world powers November 24 to curb its nuclear program in exchange for an easing of sanctions. Negotiations for a final deal are ongoing.