Tehran has provided steady political, financial, and military backing to Syrian President Bashar al-Assad as he has fought back a seven-year uprising.

On Sunday, Iranian Defence Minister Amir Hatami arrived in Syria for a two-day visit and met his Syrian counterpart Abdullah Ayoub.

"Syria is in a very, very important juncture. It is passing through the critical stage and it is entering the very important stage of reconstruction," said Hatami, in comments carried by Iranian state broadcaster IRIB.

He said it was agreed with Syria that Iran would have "presence, participation and assistance" in reconstruction "and no third party will be influential in this issue."

Since it erupted in 2011, Syria's war has cost it approximately $388 billion (334 billion euros), according to the United Nations' Economic and Social Commission for Western Asia (ESCWA).

Assad last month said reconstruction was his "top priority" in Syria, where more than 350,000 people have been killed and millions forced to flee their homes.

World powers who long called for his ouster insist reconstruction aid should only come with political transition, but fellow regime ally Russia is pressing them to provide support.

Ayoub, in comments carried by Syrian state media, championed the two countries' special relationship.

"Syrian-Iranian relations are a model for bilateral ties between independent and sovereign nations," Ayoub said.

The two countries have had strong ties for years. Iran has dispatched military forces to Syria but insists they are advisors, not fighters.

Iran-backed militias, including the powerful Lebanese Hezbollah movement, have also backed Assad's troops.

With help from them and Russian warplanes, Assad has recaptured around two-thirds of the country and is now eyeing the northwest province of Idlib.

"Idlib will return to the nation's bosom, and all Syrian soil will be cleansed of terrorism, either through reconciliation or ground operations," Ayoub said on Sunday.

He also slammed the United States, which has established military bases in Syria to fight the Islamic State group.

"The Americans are looking for a way to stay east of the Euphrates River to lock in their presence in this region," said Ayoub.

The comments came a day after a senior US diplomat, ambassador William Roebuck, visited territory around those bases and said the US was "prepared to stay" in Syria to defeat IS, but was also "focused" on ousting Iran.

According to Al-Watan, a Syrian daily close to the government, Hatami arrived with an Iranian military delegation and is expected to meet Assad during the trip.