The presidents of Russia and Turkey should act urgently to avert a "bloodbath" in Idlib Province, the last major rebel stronghold in Syria, the UN envoy to Syria has said.
Staffan de Mistura said in Geneva on September 4 that telephone talks between Russian President Vladimir Putin and his Turkish counterpart, Regep Tayyip Erdogan, "would make a big difference."
He made the comments as Syrian government forces began preparing for a major assault on Idlib, the last major enclave held by fighters battling President Bashar al-Assad in the country's seven-year war.
Russia has given Assad crucial support throughout the war in Syria, which has killed hundreds of thousands of people and uprooted millions since it began with a government crackdown on protesters in March 2011.
Turkey is backing opposition groups but has sponsored with Russia and Iran, Assad’s other key ally in the Syrian war, a series of negotiations on the conflict.
On September 4, the White House said the United States was "closely monitoring the situation" in Idlib, where it said "millions of innocent civilians are under threat of an imminent Assad regime attack, backed by Russia and Iran."
Idlib is home to an estimated 3 million civilians and the United Nations has warned that some 800,000 people could be forced from their homes by any major government offensives. The war has already killed more than 400,000 people and displaced millions.
"Let us be clear, it remains our firm stance that if President Bashar al-Assad chooses to again use chemical weapons, the United States and its allies will respond swiftly and appropriately," the White House statement also said.
U.S. Secretary of State Mike Pompeo and Turkish Foreign Minister Mevlut Cavusoglu spoke on September 4 about the Syrian conflict, and both diplomats agreed the expected military offensive in Idlib would be an "unacceptable, reckless escalation," according to State Department spokeswoman Heather Nauert.
Earlier on September 4, the Britain-based Syrian Observatory for Human Rights reported that Russian jets carried out dozens of air strikes on rebel-held areas in Idlib and other provinces, killing at least 12 civilians.
If confirmed, they would be the first Russian air strikes there in three weeks.
Meanwhile, Israeli jets flying over Lebanon struck at targets in Syria's Hama and Tartus provinces, Syrian state media reported.
SANA news agency said the country's air defenses shot down five missiles, adding that one person was killed and 12 others were wounded in the air strikes.
The observatory said the jets targeted military installations belonging to Iran.
Israel is believed to be behind a string of strikes targeting government and allied military installations in Syria.
Late on September 3, U.S. President Donald Trump warned Assad and his allies not to "recklessly attack" in Idlib.
"The Russians and Iranians would be making a grave humanitarian mistake to take part in this potential human tragedy. Hundreds of thousands of people could be killed. Don't let that happen!" Trump tweeted.
Russia rejected Trump's warning, with Kremlin spokesman Dmitry Peskov saying on September 4 that the Syrian Army was getting ready to clear a "hotbed of terrorism" in Idlib.
"The Idlib situation continues to make us feel strongly concerned in Moscow, Damascus, Ankara, and Tehran," Peskov said, adding that the presence of militants in the province was undermining the Syrian peace process and making the region a base for attacks against Russian forces in Syria.
Peskov also said the situation in and around Idlib Province will be a main item on the agenda when Putin meets with the presidents of Iran and Turkey in Tehran on September 7.
That same day, the United Nations Security Council will hold a meeting on the situation in Idlib, the U.S. ambassador to the world body, Nikki Haley, said at a news conference.
"The situation in Idlib is sensitive," Iranian state news agency IRNA quoted Foreign Minister Mohammad Javad Zarif as saying.
"We will try to remove terrorists from Idlib with the least human cost," he added.
Iran, Russia, and Syria often refer to any armed opponent of the Syrian government as a "terrorist." In the case of Idlib, an estimated 10,000 fighters with the Al-Qaeda-linked Hayat Tahrir al-Sham group are believed to be the dominant force among rebels there.