UN Syria envoy Staffan de Mistura told reporters that there was a high concentration of foreign fighters in Idlib, including an estimated 10,000 terrorists, but it would be better to set up humanitarian corridors to evacuate civilians than rush into a battle which could turn prove to be a "perfect storm".
The exercise comes amid high tension in the region, with Moscow claiming that the USA is deploying additional military assets towards Syria for a likely missile attack against Syrian government forces.
The evacuation proposal reflected rising concerns that Idlib could become the site of the latest humanitarian disaster in a country that has faced many of them during a war that has killed over 400,000 people and driven more than 5.5 million to flee overseas.
"It's very regrettable", he said.
Government forces have been massing around Idlib - Syria's only remaining rebel-held province - for days and looked poised to launch what could be the last major battle of the civil war that has torn the country apart since 2011.
"We have engaged the Russian Government and also the military at the most senior level".
Speaking at a press conference in Moscow with his Syrian counterpart Walid al-Muallem following a closed-door meeting, Russian Foreign Minister Sergey Lavrov stated that the majority of Syria had been "freed of terrorists", save for Idlib, a northeastern province bordering Turkey.
There could be no justification to use heavy weapons against them in densely populated areas, he said.
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"The United States has taken a very strong stance in the past when chemical weapons have been used".
De Mistura floated two options: one to not accelerate military escalation to allow more time for talks, and another to "allow and facilitate a credible - credible - humanitarian corridor to allow the civilian population to temporarily evacuate to a safer area".
"That area most likely is under government control, so that requires a constructive, effective government support and a United Nations presence", he said. He said he could travel to the area himself to help monitor an evacuation.
"We will practise our legitimate right in defending ourselves, but the consequences of the aggression will hit the political process definitely and everyone will be [affected]", he said.
The missile cruiser "Marshal Ustinov" is the lead ship in the exercise, which will last until September 8, according to the Russian Defense Ministry.
The ministry said the maneuvers will focus on antiaircraft, antisubmarine, and demining exercises.
Russia has this month been actively expanding its naval forces in the Mediterranean, part of what a Russian newspaper on Tuesday called Moscow's largest naval build-up since it entered the Syrian conflict in 2015.