Syrian aid workers issued an urgent call for a ceasefire and international help for nearly a million people fleeing a regime onslaught in the country's northwest on Wednesday.
The Syrian army's offensive, backed by Russian air power, has triggered the biggest wave of displaced civilians in the nine-year conflict.
At a press conference in Istanbul, the Syrian NGO Alliance said existing camps are overcrowded and civilians forced to sleep in the open as more than 900,000 people flee the violence.
"We are facing one of the worst protection crises and are dealing with a mass movement of IDPs (internally displaced persons) who have nowhere to go," the Syrian NGO Alliance said in a statement.
They are "escaping in search of safety only to die from extreme weather conditions and lack of available resources," it added.
The group said a total of $336 million was needed for basic food, water, shelter. Education resources were also needed for 280 million displaced school-aged children.
Turkey, which backs some rebel groups in Idlib, has been pushing for a renewed ceasefire in talks with Russia, eager to prevent another flood of refugees into its territory adding to the 3.7 million Syrian refugees it already hosts.
"An operation in Idlib is imminent... We are counting down, we are making our final warnings," Erdogan said in a televised speech, calling for Syrian forces to retreat behind Turkish positions in Idlib.
"Unfortunately we could not obtain the desired result during negotiations in our country and Russia, as well as on the ground," he said, adding that talks were ongoing with Moscow.
The Syrian NGOs called for the warring parties to allow safe access for humanitarian groups and for a "complete ceasefire and end to human rights violations".
The regime offensive has killed more than 400 civilians since it began in December, according to the Syrian Observatory for Human Rights.
"The violence in northwest Syria is indiscriminate. Health facilities, schools, residential areas, mosques and markets have been hit," the UN head of humanitarian affairs and emergency relief, Mark Lowcock, said earlier this week.
Regime and Russian forces have been accused of deliberately targeting hospitals and clinics, but Moscow has repeatedly vetoed Security Council resolutions.
The head of the World Health Organization said Tuesday that out of nearly 550 such facilities in northwest Syria, only about half were operational.
"We repeat: health facilities and health workers are not a legitimate target," Tedros Adhanom Ghebreyesus told journalists in Geneva.
Syrian troops have reconquered swathes of Idlib and retaken the key M5 highway connecting the country's four largest cities as well as the entire surroundings of Aleppo city for the first time since 2012.
According to the Observatory, government forces made new gains in western Aleppo province on Tuesday and were pushing towards the Sheikh Barakat mountain.
That would give them a vantage point over swathes of Idlib and Aleppo provinces, including sprawling camps housing tens of thousands of displaced people.