Iran's foreign minister who negotiated Tehran's landmark nuclear deal with world powers is visiting Lebanon on his way to Syria later this week.

Jawad Zarif arrived on Tuesday in Beirut where he is to hold talks with Lebanese officials before proceeding on to Damascus.

Iran is Syrian President Bashar Assad's strongest supporter and has been marketing itself as a key player that could help resolve Syria's crisis following the successfully brokered nuclear deal. The Syrian conflict has killed more than 250,000 people since it broke out in March 2011.

Earlier in the day, Turkey said Zarif had postponed a scheduled stop there, which was due to take place before his trip to Lebanon. There was no explanation from Ankara on the cancellation and no further details were immediately available.