This includes hundreds of thousands who were displaced from other parts of Syria - many forcibly exiled after refusing to return to living under the Assad regime as it reclaimed the country from rebel groups.
Idlib is the insurgents' only remaining major stronghold and a government offensive could be the war's last decisive battle.
At the summit in Tehran, Erdogan, Russia's Vladimir Putin and Iran's Hassan Rouhani agreed in a statement that there could be no military solution to the conflict and it could only end through a negotiated political process.
She told the Council: "If Assad, Russia and Iran continue down the path they are on, the consequences will be dire".
Turkey has renewed calls for worldwide backing for a ceasefire in Idlib, telling the United Nations security council that an all-out assault on Syria's rebel-held province would trigger a huge wave of refugees and could threaten Europe.
Iran, Russia and Turkey past year set up the Astana process, a negotiating track to end Syria's war that has largely eclipsed the UN-led peace process.
The attack occurred late Monday in the rural Tulul al-Safa area of the province, some 100 kilometres (60 miles) southeast of Damascus, the Syrian Observatory for Human Rights said.
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A Syrian regime offensive on the opposition province of Idlib could lead to the 21st century's worst loss of life.
The Russian government has openly warned the United Nations and wider worldwide community of a potential false-flag operation that could be carried out in Syria created to frame and discredit embattled Syrian President Bashar al Assad's government, it has been reported.
"An operation would result in a massacre", Erdogan says.
Erdogan's comments came just four days after meeting with his Iranian and Russian counterparts in Tehran to develop a strategy to protect Idlib's civilians, where Erdogan failed to achieve his goal, a ceasefire in the province which is home to almost 3 million people. Such a response is especially likely due to the high visibility of the Idlib situation and Washington's multiple warnings about chemical weapons use.
On Tuesday US Defense Secretary Jim Mattis said Assad has been well warned against any chemical weapons use in an anticipated assault on Idlib province. "He's been warned and so we'll see if he's wised up", Mattis added.
Haley further blamed Russian Federation and the regime for allegedly carrying out more than 100 air strikes, some of which she said were "ruthless double tap" strikes targeting first responders. "That's something we're monitoring very closely", OCHA spokesman David Swanson said.