Syria will be on the diplomatic center stage Friday as diplomats seek to avoid a possible bloodbath in Idlib province, the last region of Syria still controlled by the rebels.
The presidents of Russia, Turkey and Iran are to hold a summit in Tehran.
Russia and Iran are Syria’s closest allies and back its military, while Turkey, whose border lies along Idlib, backs the rebels. Turkey fears a refugee crisis if Syrian forces attack.
Meanwhile, the U.N. Security Council will hold an emergency session in New York.
Eight European council members issued a joint statement Thursday, saying they were "deeply concerned" a military strike in Idlib could create "potentially catastrophic humanitarian consequences for civilians."
"A full-scale military offensive in Idlib would put at risk the lives of more than 3 million civilians, including 1 million children living in the region," the statement said.
The eight nations urge Turkey, Russia and Iran to uphold the cease-fire in Idlib and make protecting civilians a priority.
Also Thursday, the new U.S. special adviser for Syria, Jim Jeffrey, said there is "lots of evidence" that chemical weapons are being prepared by Syrian forces around Idlib.
Jeffrey called the situation in Idlib "very dangerous" and said a Syrian military strike would be a "reckless escalation."
President Donald Trump has said the U.S. is watching the situation very closely.
Syrian forces have been massing on the border of Idlib, preparing for what observers believe is an imminent attack.
About 3 million people are in the province. Many of them are rebels and their families who came there after being given a chance to evacuate other former rebel-held areas before Syrian forces moved in.
The Syrian military has been urging the rebels in Idlib to surrender.
