Idlib is located in the northwestern corner of Syria.
The lion's share of the rest is the Kurdish-controlled northeast. A vital highway linking the cities of Aleppo and Damascus, known as the M5, cuts through Idlib's eastern flank.
The Observatory recorded the deaths of 64,000 hardline Islamists and jihadists, including from the Islamic State group and former Al-Qaeda affiliate factions. Another rebel umbrella group called the National Front for Liberation is backed by Turkey. With nowhere left to go, some might opt to fight till death rather than surrender. Syrian government forces have massed to the south and southwest of the province.
Most people made a dash for Syria's northern border with Turkey, with just under half seeking refuge in displacement camps, staying with local families or in rental apartments. Among the civilians are close to 1 million children, according to rights groups.
If government forces advance further towards them, they would have no choice but to move to the Turkish frontier, he added.
A full-scale air and ground offensive is likely to send waves of refugees surging toward the sealed Turkey border, coinciding with the onset of winter.
The U.N. warned last week that such an offensive would lead to the "worst humanitarian catastrophe in the 21st century".
"They did not differentiate between civilians and others", he told Reuters from a village near the Bab al-Hawa crossing with Turkey.
Speaking to reporters after a United Nations -backed humanitarian task force meeting Thursday chaired by the USA and Russia, Moumtzis said the Office for the Coordination of Humanitarian Affairs and its partners want to be ready for up to 900,000 people who could flee Idlib.
"We will not act in the way the USA -led coalition acted in Mosul or in Raqqa when there were no negotiations about local cease-fires with opposition groups", he said.
Syrian President Bashar al-Assad has now set his sights on Idlib, and his forces have stepped up bombardment of the densely populated province since the beginning of the month.
Twice before, the USA has resorted to missile strikes in response to chemical weapons attacks, only to see them used again.
Also Friday, The Elders, an global non-governmental organization of public figures, called on Russia, Turkey and Iran to work "hand-in-hand to prevent heavy civilian casualties in Syria's Idlib region".
President Tayyip Erdogan will hold talks in Russia on Monday with Vladimir Putin to discuss the Syrian crisis, 10 days after similar talks in Tehran, Turkish and Russian officials said. He said it would amount to "indiscriminate attacks to wipe out its opposition and not a genuine or effective campaign against terrorism".
"What happened was destruction all over, burning, something you can't describe", said Ali al-Mheymid, 50, who escaped the village of Sarjah in Idlib province with his family last week.
Proposals include urging Hay'at Tahrir al-Sham to dissolve itself or join the Turkey-backed rebels.
Russian Foreign Minister Sergei Lavrov said that Moscow would keep bombing militant targets in Idlib if need be, but would also open humanitarian corridors to allow civilians to flee, the Interfax news agency reported.
The most pressing issue on the table is the avoidance of the looming Syrian offensive in Idlib.
Russian Federation has accused the White Helmets of staging a chemical attack in Idlib in order to provoke a Western military intervention in Syria.