The U.N. Office for the Coordination of Humanitarian Affairs (OCHA) said an all-out military assault on the last major stronghold of active opposition to President Bashar al-Assad could set 800,000 people to flight.
"We've been in consultation with the British and the French, who joined us in the second strike, and they also agree that another use of chemical weapons will result in a much stronger response", Bolton was quoted by The Wall Street Journal as saying.
Russian Federation hopes for a peaceful resolution of the situation in Syria's rebel-held province of Idlib but believes it is up to Turkey to separate Islamist militants from the moderate opposition, Russia's Syria envoy said on Tuesday.
It is unclear when the offensive will formally begin and what impact the fall of Idlib could have on Turkish-controlled Afrin and the northern provinces controlled by the US-backed and Kurdish-led Syrian Democratic Forces (SDF).
A further complicating factor for Turkish aid agencies is that many civilians themselves are now carrying arms for protection, making it harder to distinguish them from fighters.
Yesterday, the United Nations warned that a large-scale military operation against Idlib could create "the worst humanitarian catastrophe with the biggest loss of life in the 21st century".
Syrian Foreign Minister Walid Muallem spoke to Russia Today: "We do not want to come into conflict with Turkey but they must understand that Idlib is Syrian soil!"
He acknowledged that there were many rebels and fighters from "terrorist" groups in the province, but stressed that "there are 100 civilians, majority women and children, for every fighter in Idlib".More news: Robert Scott, economist, says fears over Donald Trump tariffs overblown
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USA officials have said in recent days they have evidence that Syrian government forces are preparing chemical weapons ahead of a planned assault on Idlib.
Assad's regime has been repeatedly accused of using chemical weapons during the conflict and a year ago US President Donald Trump unleashed Tomahawk missiles against the regime's Shayrat airbase following an attack that killed more than 80 people.
He said this requires time and patience and is what Turkey has been trying to achieve in its separation efforts in Idlib.
Idlib residents hope Turkey's presence in the province might prevent a major assault by regime forces and Ankara's relationship with Iran and Russian Federation could lead to a new ceasefire.
Turkey's permanent representative to the United Nations, Feridun Sinirlioğlu called on Tuesday for an immediate and complete ceasefire that will include the cessation of all military operations in Syria's Idlib.
"In Idlib, we're watching very closely what the Assad regime, aided and abetted by the Iranians and the Russians are up to", Mattis told Pentagon reporters.
A newly displaced Syrian child arrives with his family at a refugee camp in Atimah village, Idlib province, Syria, Sept 11, 2018.
"We go wherever it's safe", said the man in his 30s.