Russian President Vladimir Putin however, said that he was against a ceasefire because Nusra Front and Islamic State of Iraq and the Levant (ISIL) fighters located there were not part of peace talks.
The United States on Wednesday warned an all-out offensive in Idlib would be a "reckless escalation" of the conflict.
In a statement, Treasury Secretary Steven Mnuchin said that "millions of innocent people in Idlib province are now under the threat of imminent attack from the Assad regime, backed by Iran and Russian Federation, under the pretense of targeting ISIS".
After his meeting with Rouhani, Erdoğan and Putin also held a one-on-one meeting.
"Turkey's aim in Idlib has been to avoid a new, destabilizing conflict on its border".
More than half of Idlib is controlled by militants from Syria's former Al-Qaeda affiliate, Hayat Tahrir al-Sham (HTS), while much of the rest is held by rebels backed by Turkey.
Although the military campaign against the Islamic State has been almost completed, the administration has redefined its goals to include the exit of all Iranian military and proxy forces from Syria, and establishment of a stable, nonthreatening government acceptable to all Syrians and the global community.
A Syrian woman sits on a straw mat next to children outside a tent at a camp for displaced civilians fleeing from advancing government forces near the village of Sarman in the rebel-held northwestern Idlib province, September 1, 2018.More news: Chaos mars hearing for Trump Supreme Court pick
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Turkey backs numerous rebel groups in the province but recently moved toward its negotiating partners in declaring that the Al-Qaeda affiliate Hayat Tahrir al-Sham, formerly known as the Al-Nusra Front, is a "terrorist organization" that should be eliminated.
"We have killed, we are killing and we will kill terrorists. whether that be in Aleppo, Idlib or other parts of Syria".
The Russian military says it has shot down dozens of hostile drones.
As Putin and Erdogan were arriving in Tehran, the Syrian Observatory for Human Rights said air strikes were targeting positions belonging to rebel groups in the northern Hama and southern Idlib provinces.
Assad's government has been massing thousands of troops in preparation for an assault. "The Turks have shown a great deal of resistance to an attack".
Russian Foreign Ministry Spokeswoman Maria Zakharova said that barrels of chlorine and munitions had been delivered to Idlib, while members of the White Helmets, which had been involved in the staged chemical weapons incident in the Syrian town of Douma in April, were getting their cameras ready.
The White House has warned that the United States and its allies would respond "swiftly and vigorously" if government forces used chemical weapons in the widely expected offensive. Sources said he cautioned that he didn't want to hear in October that the military hadn't been able to fully defeat ISIS and needed to stay.
Aid groups have warned that any military offensive in Idlib could spark one of the worst humanitarian disasters of Syria's seven-year civil war.