Iran is backing Syrian President Bashar al-Assad in his country's civil war, along with Russian Federation and Lebanese terror group Hezbollah. "The Russians and Iranians would be making a grave humanitarian mistake to take part in this potential human tragedy", Trump said in a tweet on Monday.
Their comments came after Iranian Foreign Minister Mohammad Javad Zarif on September 3 called for militants to be "cleaned out" of Idlib on a visit to Damascus ahead of an upcoming summit between the leaders of Iran, Russia, and Turkey in Tehran on September 7 to discuss Idlib.
"Syria's territorial integrity should be safeguarded and all tribes and groups, as one society, should start the reconstruction process, and the refugees should return to their homes", Zarif said, according to Iran's Fars news agency. Israel has said it will not tolerate a permanent Iranian military presence in Syria, especially near the frontier between the two countries.
At least eight Iranian forces were killed by an US-led global anti-ISIS coalition air strike near the Al Tanf military base, according to a UK-based conflict monitory.
Thousands of government troops have been surrounding the area, preparing for what appears to be a major assault.
Russia, which has yet to comment on the latest statement from the USA leader, has been working for weeks to establish humanitarian corridors in Idlib province.
Assad has vowed to defeat the opposition in its last refuge in the northwestern province if the rebels do not surrender to government rule.
Further Iranian engagement in Syria meanwhile risks drawing Israel deeper into the conflict.
According to a CNN report late last week, the USA has put together an initial list of Syrian chemical weapons facilities that could be targeted with airstrikes if Syria were to launch a new chemical weapon attack.