Fears are growing that a government offensive to retake the last major region controlled by rebels is imminent. It has also consistently denied using chemical weapons over the course of the foreign-backed militancy, which broke out in the country in 2011.
Any offensive on Idlib could raise tensions with Turkey, which maintains observation posts around rebel territory as part of a "de-escalation deal" with Russian Federation and Iran, another ally of the Syrian government.
Syrian's foreign minister said on Thursday, that government forces will "go all the way" in the northern region of Idlib and that Damascus's main targets were al-Nusra militants.
Russian Foreign Minister Sergey Lavrov, right, welcomes Syrian Foreign Minister Walid al-Moualem for talks in Moscow on Thursday.
"By holding talks with Americans, we are looking to clear Manbij in Syria from terrorists", he added.
At the weekend, Russian Federation repeatedly warned that Syrian-based terrorists were planning the attack in the militant-held province, which is home to almost three million people. The Kremlin agreed the drill may be connected with the situation in Syria's Idlib governorate.
Idlib and surrounding areas outside government control are home to three million people, of whom 1.8 million are displaced.
"It would be a tragic irony frankly if at nearly the end of. a territorial war inside Syria, we would be witnessing the most horrific tragedy to the largest number of civilians", he said.More news: Taylor Swift on Aretha Franklin
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"That area most likely is under government control, so that requires a constructive, effective government support and a United Nations presence", he said.
Staffan de Mistura called for humanitarian corridors to be set up to allow civilians to be evacuated temporarily.
"It would be quite tragic at this stage, having seen how hard the seven years (of Syria's war) have been".
"We definitely intend to discuss it very intensely with the government", de Mistura said.
While he stressed the legitimacy of battling such "UN-identified terrorists", he insisted efforts to defeat them did not justify putting the lives of some 2.9 million people in the area at risk.
"It is necessary to disassociate the so-called moderate opposition from terrorists and at the same time prepare an operation against them while minimising risks for the civilian population", Lavrov said.
Both ministers warned against any "act of aggression" from western countries, particularly from the United States, citing staged chemical attacks by "provocateurs" such as the Syrian civil defence group the White Helmets being used as a pretext for such assaults.
De Mistura echoed that concern.