Iran's president will make his first official trip to Saudi Arabia on Saturday.
An Iranian official said President Mahmoud Ahmadinejad would leave on Sunday after talks on regional affairs.
Saudi Arabia, a US regional ally, is leading a diplomatic drive to curb Tehran's growing influence in Lebanon and Iraq. Saudi Arabia has accused Iranian-backed Shia militias of sectarian killings of Sunni Iraqis.
Saudia Arabia, a Sunni bastion, and other US-allied Arab governments are also concerned that Shia Muslim Iran is gaining influence in Lebanon by supporting Hizbullah in its conflict with the US-backed government of Fouad Siniora.
Saudi Arabia and Israel share US suspicions that Iran is trying to develop nuclear weapons under cover of its nuclear energy programme. Tehran denies the accusations.
Saudi and Iranian officials have met several times to mediate between Lebanese opposition forces led by Hizbullah, which is also backed by Syria, and the Siniora government. But these talks appear to have made little headway.
A Lebanese political source in Beirut said Iran wanted to break the ice between Saudis and Syrians - a key element in defusing Lebanon's crisis - before an Arab League summit set for Saudi Arabia at the end of March.