Russian warplanes struck rebels in Syria’s last major opposition stronghold on Tuesday, forcing the Trump administration to confront a looming regime offensive that is expected to deliver a fatal blow in the seven-year conflict and hand Moscow a diplomatic victory.
The Trump administration issued a coordinated call for Russia, Iran and Syria to avoid a military assault on Idlib. President Trump, Secretary of State Mike Pompeo, United Nations Ambassador Nikki Haley, and Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, all warned of a potential catastrophe if the battle goes forward.
Moscow has dismissed U.S. concerns that Syria again will use chemical weapons during the offensive, a move that has twice led Mr. Trump to order limited airstrikes targeting the Syrian regime. The Kremlin’s response has fueled widespread skepticism in Washington about Moscow’s intentions, and raised fears that Russia will give Syria a free hand to use chemical weapons on civilians as Syrian forces prepare for a battle that could deliver a crippling blow to rebels who have been fighting the regime.
“We will find out and learn the extent to which the U.S. has power short of deploying military force,” said Nicholas Heras, a Syria expert at the Center for a New American Security. “The Trump administration has one more chance to carve a line in the sand.”
U.S. officials have outlined no plans to intervene militarily in an assault, but the Trump administration has warned that it could again hit the Syrian regime if it uses chemical weapons.
“If they want to continue to go the route of taking over Syria, they can do that, but they cannot do it with chemical weapons,” Ms. Haley told reporters at the United Nations.
Chief U.S. concerns in Syria are the presence of Islamic State fighters and the Iranian-backed military units. The U.S. has around 2,000 troops in northeastern Syria to help fight the extremist group.
The U.N. and other international bodies have warned that an all-out assault could lead to a humanitarian disaster akin to the fall of Aleppo, which brought suffering unlike anything seen during the Syrian war to a population much smaller than that of Idlib. In contrast with Aleppo, Idlib’s displaced will have few places to run, as Turkey has denied entry to Syrian refugees and the regime has gained ground.
“Civilians had been anxiously hoping for world powers to agree [on] a diplomatic solution that could avoid an assault that would put thousands of innocent lives at risk,” said Lorraine Bramwell, the International Rescue Committee’s Syria country director.
Russia’s Defense Ministry confirmed Wednesday that its war planes had hit rebel targets in the Syrian region of Idlib.
Russian Defense Ministry spokesman Gen. Igor Konashenkov said the aircraft—Su-34 jet fighter-bombers and a Su-35—had used high-precision munitions to destroy several of the rebels’ munitions stocks as well as a warehouse where rebels had been manufacturing makeshift drones that have attacked Russia’s Hmeimim airbase since the start of this year.
“Four airplanes under the command of the Russian Air Force group at Hmeimim carried out strikes in Idlib with high-precision munitions,” said Mr. Konashenkov.
As the airstrikes intensified, Mr. Trump warned on Tuesday that an attack on Idlib “would be a reckless escalation of an already tragic conflict that would risk the lives of hundreds of thousands of people.”
Mr. Trump warned that the U.S. would “respond swiftly and appropriately” if Syrian President Bashar al-Assad used chemical weapons.
U.S. officials said they have picked up indications that Syria is preparing to use such weapons, as it did in Idlib province a year ago and earlier this year in a Damascus suburb. In both cases, the U.S. launched limited airstrikes on Syrian regime targets that were largely meant to deter Mr. Assad from using chemical weapons and to destroy his ability to carry out such attacks.
The Assad regime is tightening its grip on the entire country after emerging victorious in the long war, retaking in recent months the Damascus suburb of Eastern Ghouta and most of the southern provinces. It left the north for last as the battle there is complicated by diverging interests of several foreign powers and the largest presence of antigovernment fighters.
Leaders of Russia and Iran, Mr. Assad’s main backers, along with Turkey’s president are set to meet in Tehran on Friday for talks on what is expected to be the last chapter in the war. Northwestern Syria is under a trilateral cease-fire deal brokered last year among the three countries, but that hasn’t prevented the regime and Russia from regularly launching strikes in the area.
Idlib is home to nearly three million people, according to some estimates, about half of whom have already been displaced from other parts of Syria. There is no exact information on rebels, but Western officials estimate the number to be at least 20,000.
The drumbeat for what will likely be the final major battle of Syria’s conflict has been growing for weeks. In August, the Syrian regime pounded towns and the countryside in Idlib, and distributed pamphlets urging locals to surrender. Meanwhile, rebel factions inside Idlib have in recent weeks detained dozens of people suspected of negotiating surrender with the regime or its Russian backers.
A commander for the Ahrar al-Sham militant group said last week that rebels in Idlib were making preparations to defend the province against an attack. “The battle for the north will be hell for the Russians, and not like other areas,” the commander, Jaber Ali Bashar, said.
Russia has bombarded Idlib over the course of the war, but Tuesday’s strikes—about 30 targeting an area 25 miles west of Idlib city—were the first large-scale raids in three weeks, according to the White Helmets civil-defense group. At least 17 civilians were killed in the attacks, including five children, the group said.
The Russian Ministry of Defense wasn’t immediately available for comment. On Tuesday, Kremlin spokesman Dmitry Peskov warned that Syrian armed forces were readying to act in Idlib, where he said militants from across Syria had congregated. The Syrian government didn’t respond to a request for comment.
—Vivian Salama, Nour Al Akraa, Nancy A. Youssef, Farnaz Fassihi
and Michael R. Gordon contributed to this article.
Corrections & Amplifications
Syrian government forces used chemical weapons in Idlib a year ago and in a Damascus suburb earlier this year. An earlier version of this article incorrectly said the attacks were two years ago and last year, respectively. (Sept. 5, 2018)