U.S. officials claim they are anxious that an impending assault by Syria forces on the terrorists in Idlib could involve the use of chemical weapons, an issue that Damascus has dismissed as false lies by Washington.
"Throughout their trip, Ambassador Jeffrey... will also address Russia's specious allegations of worldwide plans to stage a chemical weapons attack in Syria", the release said on Friday.
The looming battle for Idlib in northwestern Syria may be the last in the bloody seven years of conflict, which have backed hundreds of thousands of civilians into this deadly corner of the country with nowhere to run.
Lavrov got backing from an unexpected source on August 31 for the government's avowed plans to "liquidate" the extremist Al-Qaeda group, Hayat Tahrir al-Sham, previously known as Al-Nusra Front, which includes many recruits from foreign countries.
And that reality, he told AFP, is that "Assad is advancing on the ground, aided by Iran by land and Russian Federation by air", while the United States places its hopes on a UN-backed Geneva peace process that might best be described, he said, as "moribund".
Turkey has been keeping a wary eye on the possibility of the Idlib offensive, as it seeks to bring peace to Syria along with Russian Federation and Assad's other main ally Iran.
We have been aware of that since the very beginning.
In this December 20, 2012, file photo, Syrian refugees, who fled their home in Idlib due to a government airstrike, look out of a vehicle's window just after crossing the border from Syria to Turkey in Cilvegozu, Turkey.
It bracketed HTS as a variant name for Al-Nusra Front.
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The government has been accused of attacking civilians with chemicals in previous operations, including in Douma near Damascus and in Khan Sheikhun, in Idlib.
The civil war in Syria seems to be nearing its end, yet officials have been voicing their concerns that an offensive toward Idlib would end in catastrophe and ignite new conflicts in the region.
"At our meeting with Nasr Al-Hariri, president of Syrian Negotiations Commission, we exchanged views on recent developments in Syria, including Idlib and also the period ahead concerning the political process", Cavusoglu wrote on his Facebook page.
The International Crisis Group, a Brussels-based think tank, said an all-out assault on Idlib and its catastrophic consequences could still be avoided.
Turkey says it is seeking to ward off a full-scale offensive, urging Russian Federation and Iran to allow more time to separate "radical militants" from the armed groups it has backed. Western countries immediately blamed Damascus for the attack.
Though the group claims to have no direct ties to al-Qaida, it's considered a terrorist group by the United States and the United Nations.
President Recep Tayyip Erdogan will travel to Iran to meet with his Russian and Iranian counterparts Vladimir Putin and Hassan Rouhani, state-run TRT Haber television said.
She said violence could force as many as 800,000 people to flee in one of the Syrian war's largest displacements yet.