Syrian Foreign Minister Walid al-Muallem was to visit Tehran on Sunday for talks with Iranian officials, the Iranian foreign ministry said in a short statement.
The trip was not previously announced.
It comes as Syrian troops battle rebels in Syria's second city of Aleppo in an offensive that world powers fear could result in heavy civilian casualties and spark a humanitarian disaster.
The foreign ministry said Muallem would meet Foreign Minister Ali Akbar Salehi and they would give a joint news conference at around 0930 GMT.
Iranian news agencies reported that Muallem would see various Iranian officials.
The ISNA news agency said, without giving a source for its information, that one of those officials would be the head of Iran's supreme national security council, Saeed Jalili, who is close to supreme leader Ayatollah Ali Khamenei.
Iran is Syria's staunchest Middle East ally. It has sent humanitarian aid and provided diplomatic backing, but denies reports it has also sent military support to Damascus.
Muallem's visit follows that of a Syrian delegation led by Deputy Prime Minister Omar Ghalawanji who held talks with Iranian officials on Wednesday said to focus on boosting economic cooperation.
One of Iran's vice presidents, Ali Saidlou, was quoted as telling Ghalawanji in a meeting that day that Syria's enemies "will fail" in their bid to pressure Damascus over the uprising, now in its 17th month.
A top Iranian military official, Brigadier General Masoud Jazayeri, the deputy chief of Iran's joint armed forces, stated on Tuesday that Syria's allies "will not allow regime change" and warned they would land "decisive blows" on Damascus's enemies -- "in particular to the despised Arabs." Jazayeri defined Syria's enemies as "the evil governments of America, Turkey, Qatar, Saudi Arabia and other allies of the terrorists" fighting the regime of Syrian President Bashar al-Assad.