Ankara says Assad's regime has the capacity to make chemical weapons and needs to be stopped.
Turkey said it has concrete evidence that deadly sarin gas was used in the Idlib attacks and there should be measures to prevent the Syrian regime from using the chemical weapons they still have in stock.
"We have stressed that the Assad regime may also attack Idlib, and we need to take measures for this," Turkey's Foreign Minister Mevlut Cavusoglu told journalists on the sidelines of a G7 meeting in Italy.
"We have also stressed that Russia should be persuaded on a Syria without Assad," he said.
Foreign ministers from the world's seven most industrialised nations also agreed that there can be no peace in war-torn Syria with Assad in power.
Ending the conflict that is now in its seventh year has taken centre stage after a sarin gas attack killed 87 people and injured over 400.
Ankara's Health Minister Recep Akdag on Tuesday said sarin was detected in blood and urine samples taken from victims.
Western nations blame Assad for the attack and US President Donald Trump responded by firing cruise missiles at a regime air base. Russia has stood by Assad, who denies involvement.
US Foreign Secretary Rex Tillerson took off for Moscow from the G7 on Tuesday. He is expected to try to persuade Russia to abandon Assad.
On Monday, Tillerson said Washington will stand up against anyone who commits crimes against humanity, referring to last week's attack.