The United States has warned Damascus and Moscow that it views any military assault on Syria's last rebel-held province in coming days as an escalation of the seven-year Syrian civil war.
The warning from U.S. Secretary of State Mike Pompeo on August 31 came as rebels in Syria's Idlib province bordering Turkey blew up bridges and dug trenches in preparation for an all-out government assault promised by the leaders of both Syria and Russia, which is providing air support for Syrian ground forces.
"The U.S sees this as an escalation of an already dangerous conflict," Pompeo said on Twitter in a post that also lambasted Russian Foreign Minister Sergei Lavrov for defending Syria's assault plans.
"The 3 million Syrians, who have already been forced out of their homes and are now in Idlib, will suffer from this aggression. Not good. The world is watching," Pompeo said.
The United Nations has warned that a major military operation in Idlib could displace another 800,000 people in a war that has already killed more than 400,000 people and displaced millions.
Lavrov has said the Syrian government has every right to push rebels out of Idlib, including an estimated 10,000 fighters in an Al-Qaeda affiliated group that is believed to be the dominant rebel force in the province.
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.
The UN envoy for Syria, Staffan de Mistura, told reporters in Geneva that "no one doubts that Al-Nusra and Al-Qaeda are terrorists...and terrorists identified by the UN need to be defeated." But de Mistura continued to plead for protection for the millions of civilians who could be caught up in the battle.
Russian military leaders have said their forces are providing a humanitarian corridor for civilians to leave the province, and they also are attempting in talks with Turkey to separate out what they have called the "terrorists" from more moderate opposition groups that have Ankara's backing.
While Russia and Syria in the past have often have referred to all of their armed opponents as "terrorists," in the case of Idlib, they appear to be making a distinction in a bow to Turkey, which provides backing for many of the more moderate Sunni rebels in the province and which has joined Moscow and Tehran in sponsoring Syrian peace negotiations in the past year.
With a major battle over Idlib seemingly only days away, the U.S. State Department said on August 31 that it is sending the new U.S. special representative for Syria, James Jeffrey, to Israel, Jordan, and Turkey on his first official trip abroad from September 1 to 4.
Jeffrey and his delegation will "underscore that the United States will respond to any chemical weapons attack perpetrated by the Syrian regime," and will "address Russia’s specious allegations of international plans to stage a chemical weapons attack in Syria," the department said.
Russia and Syria have denied planning any chemical attacks and have charged that the extremist Hayat group -- with backing from the West -- is planning to stage one and then blame it on the government, creating a pretext for Western air strikes.
The latest exchange of warnings between Washington and Moscow comes as war monitors say thousands of Syrian government troops and allied fighters have been amassing in areas surrounding Idlib in preparation for an assault.
The Britain-based Syrian Observatory for Human Rights said Syrian forces have deployed at least 2,000 armored vehicles along the front lines surrounding Idlib and Hama.
The area, which has been controlled by rebels since 2015, has been targeted by government and Russia air and artillery strikes for months, devastating infrastructure such as schools and hospitals.