The statement on the call, attributable to State Department Spokeswoman Heather Nauert, takes a stronger position against than the one taken by US President Donald Trump the day prior.
"President Bashar al-Assad of Syria must not recklessly attack Idlib Province. The Russians and Iranians would be making a grave humanitarian mistake to take part in this potential human tragedy," Trump tweeted on Monday. "Hundreds of thousands of people could be killed. Don’t let that happen!"
Now, it appears that the State Department is expanding the White House's red line. While Trump cautioned against a "reckless attack," the State Department, in conjunction with the Turkish Foreign Ministry, is calling "any Assad military offensive" in Idlib "unacceptable."
Pompeo and Cavusoglu "agreed that any Assad regime military offensive in Idlib would be an unacceptable, reckless escalation of the conflict in Syria," the statement reads.
As the Syrian government, backed by Russian air power, has liberated major cities and districts from the jihadists since the start of the war more than seven years ago, they have allowed the militants to evacuate into Idlib. Now, there are fears the province could be the site of a chemical attack, with the UN special representative for Syria warning that militants there are capable of producing weaponized chlorine and Russia saying it has evidence of plans for chemical provocations by jihadists.
On Friday, the United Nations Security Council will convene to discuss the situation in Idlib, US Ambassador to the UN Nikki Haley told reporters on Tuesday.