EU foreign policy chief Federica Mogherini is in Tehran for talks on the situation in Syria with senior Iranian officials before heading to Saudi Arabia.
Mogherini met with President Hassan Rohani and Foreign Minister Javad Zarif in an effort to achieve a breakthrough in the conflict, in which regional rivals Iran and Saudi Arabia have taken opposite sides.
Mogherini was set to travel to Riyadh later on October 29 to hold talks with Saudi leaders.
Her trip comes a day after the foreign ministers of Russia, Syria and Iran met in Moscow to discuss the Syrian crisis and the situation in the besieged city of Aleppo where Russia has been conducting air strikes.
Moscow and Tehran both support Syrian President Bashar al-Assad.