Iranian Foreign Minister Mohammad Javad Zarif has said that armed groups must be "cleaned out" of Idlib province in northwestern Syria, Iranian media reports.
Zarif made the remarks while visiting Damascus on Monday, where he arrived for talks with Syrian government officials.
The top Iranian diplomat was scheduled to hold meetings with President Bashar al-Assad and Prime Minister Imad Khamis on bilateral relations and the latest developments in the war.
"All of Syrian territory must be preserved and all the sects and groups should start the round of reconstruction as one collective and the displaced should return to their families," Zarif said, according to Fars news agency.
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"And the remaining terrorists in the remaining parts of Idlib must be cleaned out and the region should be placed back under the control of the Syrian people," Zarif added.
Syrian government forces, backed by Iran and Russia, seek to conduct an offensive on Idlib, controlled by various rebel groups.
They have been massing around the last rebel bastion.
Zarif's visit comes after Amar Hatami, Iran's defence minister, travelled to Damascus and signed an agreement for defence cooperation with his Syrian counterpart Ali Abdullah Ayoub. Hatami also met Assad duding his trip.
Iranian forces have backed Assad in the country's seven-year-old civil war by providing steady political, financial, and military support during this period.
'Iranian advisers to stay'
Separately, Iran's military attache to Damascus told Iranian media on Tuesday that the country's military advisers would remain in Syria under a defence agreement signed this week.
"The continued presence of Iran's advisers in Syria is one of the areas covered in the defensive-technical agreement between Tehran and Damascus," said Brigadier-General Abolghasem Alinejad, according to the Fars and Tabnak news agencies.
Javad Zarif visited Turkey last week and met President Recep Tayyip Erdogan, who has been a staunch supporter of Syria's rebel forces against Assad.
Russia and Iran, which support Assad, and Turkey have been in close cooperation over Syria in order to find a solution to the conflict.
Iranian, Russian and Turkish presidents are scheduled to meet in Tehran to discuss the latest developments in Syria in early September.
Since Russia military intervened on Assad's behalf in 2015, the regime has regained much of the territory lost to fighters in the early years of the war.
Syria's war has left more than 350,000 people dead and displaced millions since it broke out with the brutal repression of an initially peaceful uprising in 2011.