Russian and Syrian regime warplanes launched airstrikes on rebel-held territory on Sunday in an attempt to fend off advances made by antigovernment forces that included a stunning assault on Aleppo .
The warplanes struck the northwestern city of Idlib, according to local rescue workers and Russian state news agency TASS. The Russian military said it was intensifying strikes on rebel supply lines.
The counterattack comes after Syria’s antigovernment rebels captured most of the city of Aleppo in a setback for the government in Damascus and its allies Russia and Iran. The rebel offensive is the most significant change in years in the balance of power in Syria, a conflict that became an arena for competition among world powers, also drawing in the U.S., Turkey, Israel and an array of other outside actors.
The rebel military command said it struck government forces north of the city of Hama, another important population center and another sign of a rapid collapse by forces loyal to President Bashar al-Assad . The Russian military said reinforcements for the regime arrived in Hama, according to TASS.
The Syria Civil Defense, an independent rescue organization also known as the White Helmets, said Sunday it was expanding its operations into areas newly retaken by the rebels. Eight civilians, including two children, were killed and 63 injured in the airstrikes by Syrian forces in Idlib, the group said Sunday.
United Nations Special Envoy for Syria Geir O. Pedersen said that “the latest developments pose severe risks to civilians and have serious implications for regional and international peace and security.” He noted that the main rebel group leading the advance, Hayat Tahrir al-Sham, is designated a terrorist organization by the U.N. Security Council.
The rebel offensive, meanwhile, poses new questions for U.S. and Western policy toward Syria. HTS is also designated a terrorist organization by the U.S. due in part to its past ties to al Qaeda. The group, previously known as the Nusra Front, said it broke with al Qaeda in 2016.
White House national security spokesman Sean Savett said Assad’s reliance on Russia and Iran and its refusal to negotiate an end to the conflict had resulted in a collapse of regime lines. “At the same time, the United States has nothing to do with this offensive” led by HTS, he said.
The retreat by government forces from Aleppo and surrounding areas poses the most serious challenge in years to the Assad regime, whose strategy is based on controlling the population centers in western Syria even as it has lost its grip on other, more rural parts of the country.
Russia launched airstrikes in rebel-held territory in recent days, while media affiliated with pro-Iran militias said Assad’s forces were sending reinforcements to the front lines. Neither appeared sufficient to stop an attack by rebels who had waited for years for an opportunity to strike.
Assad’s regime is a key partner for Russia, which has navy and air bases in Syria that are its foothold in the Mediterranean. For Iran, Syria is a symbol of its long effort to spread its influence in the region and a strategic location abutting its arch-opponent, Israel.
For years, Assad has depended on help from Russia and Iran for the survival of his regime. Russia intervened in the war in 2015, launching airstrikes that helped him roll back rebel advances and reclaim control of Aleppo in 2016 after part of it fell to antigovernment forces.
Iran and its allies have also played an essential role in the regime’s survival, sending military advisers and militia forces including those of Lebanon’s Hezbollah movement to help crush the rebellion that began with a popular uprising demanding Assad’s removal in 2011.
The government in Damascus acknowledged on Saturday that at least some of its forces had retreated from Aleppo, with the Defense Ministry saying that it had engaged in a “strategic redeployment” to reinforce its lines and prepare a counterattack. The statement said dozens of government soldiers had been killed in fighting across northwest Syria and that opposition forces had entered significant portions of Aleppo.
The rebel offensive comes as Assad’s allies are under increased pressure. Russia has poured military resources into its invasion of Ukraine, and Iran and its allied militias have suffered severe setbacks during an Israeli military offensive in both Lebanon and Syria. Israel agreed to a fragile cease-fire in Lebanon in the past week.
It also comes in the run-up to the second administration of President-elect Donald Trump , who previously imposed a policy of pressure on Iran and launched airstrikes against Syrian government military assets.
Write to Jared Malsin at jared.malsin@wsj.com
