The leaders of Turkey, Russia and Iran met today at a summit in Tehran to discuss the future of Idlib, as many fear a large-scale massacre could soon begin. The city is the only remaining major opposition-held enclave in Syria and regaining control of it is a main priority for the brutal Syrian regime. This is despite the fact that in May 2017, it was designated a “de-escalation zone” by the three leaders.
With the Syrian military, unable to stand on its own feet, world leaders are again bypassing Assad and instead addressing his backers Russia and Iran to hold off any such attack in the hope of a ceasefire. Speaking at the summit, Turkey’s President Erdogan echoed the UN’s earlier warning of a catastrophe, saying:
“We never want Idlib to turn into a bloodbath. Any attack launched or to be launched on Idlib will result in a disaster, massacre and a very big humanitarian tragedy.” 
Erdoğan says Turkey cannot leave Syria's Idlib to Assad’s mercy https://www.yenisafak.com/en/video-gallery/world/erdogan-says-turkey-cannot-leave-syrias-idlib-to-assads-mercy-2196025
Posted by Yeni Şafak on Friday, 7 September 2018
The “rebels” are made up of various factions, some of which are backed by Turkey.  However the main concern is the large civilian population of 3 million, with UN official estimating that up to 800,000 people could be displaced and thousands killed if the anticipated full-scale assault takes place.
The devastating seven-year old war has already seen more than half a million killed and 11 million displaced, resulting in major refugee crises across the region and Europe. Turkey, which has recently stood firm amidst US attempts to attack their economy, has already taken in over 3.5 million refugees and fears it could not accommodate any more.
Meanwhile the US government has warned that it has evidence that the Syrian regime and its partners are preparing chemical weapons ahead of their offensive. The new US envoy for Syria said:
“I am very sure that we have very, very good grounds to be making these warnings. Any offensive is to us objectionable as a reckless escalation. There is lots of evidence that chemical weapons are being prepared.”
“I think the last chapter of the Idlib story has not been written. The Turks are trying to find a way out. The Turks have shown a great deal of resistance to an attack.” 
Russian forces have continued to bomb the area in recent days, and both President Putin and his Iranian counterpart Rouhani have thus far disregarded any calls for a peaceful conclusion, showing their attendance at the summit to be a futile exercise.