A minivan drives past a portrait of Syrian President Bashar al-Assad in Damascus on April 7, 2017. U.S. warships fired a barrage of cruise missiles at a Syrian air base in response to what President Trump called a “barbaric” chemical attack he blamed on Assad’s government. (Louai Beshara/AFP/Getty Images)

Just a few days ago, Syrian President Bashar al-Assad looked like he had little to fear. 

After six years of war, his army had penned what remained of Syria’s armed rebellion into shrinking swaths of territory, and European leaders were preparing for a conference that could fund the reconstruction of his war-shattered country. 

That sense of security appeared shaken Friday after the U.S. military launched a raft of missile strikes at a Syrian military airfield in retaliation for a chemical attack that killed scores of civilians on Tuesday. The images of lifeless bodies splayed across the ground drew international condemnation and dragged the Syrian army’s tactics back into the spotlight.

“The difference between now and one week ago is that Assad and his backers had reasonably concluded they could fight their war however they wished, with impunity, and that the United States was a nuisance but not a threat,” said Faysal Itani, a senior fellow at the Atlantic Council, a think tank based in Washington.

The missile strikes, authorized by President Trump, marked a significant escalation of American engagement in Syria, broadening the U.S. role beyond the fight against the Islamic State militant group.

(Louisa Loveluck, Jason Aldag/The Washington Post)

The operation contrasted sharply with the Obama administration’s policy toward Syria’s crushing war, which was characterized by strong rhetoric but little political appetite to back words with force.

“Now, we can say that when the United States takes an official position on an issue . . . in this conflict, its rivals will have to factor that into their plans,” Itani said.

Forces backed by the Syrian government recaptured the northern city of Aleppo in December, dealing a heavy blow to what remained of the non-jihadist armed opposition and leaving ­Assad’s troops in control of every major urban center. Although international outrage has largely focused on the government’s use of chemical weapons, monitoring groups say deadlier still are its crudely fashioned barrel bombs that continue to shatter opposition-held areas, despite a notional cease-fire that was meant to have taken hold across the country. 

The missiles struck the Shayrat air base in the western province of Homs about 3:40 a.m. local time, officials said, killing 13 people in the military facility and its surrounding areas. Syrian military aircraft are believed to have flown from the base on sorties during which they dropped a nerve agent on the opposition-controlled town of Khan Sheikhoun on Tuesday.

The Syrian Observatory for Human Rights, a Britain-based monitoring group, said a general was among those killed in the missile strikes, which caused extensive damage to more than a dozen hangars and a fuel depot.

Witnesses described ambulances racing toward the airfield, where a huge fire was blazing. Video aired later Friday on Syrian state television showed several large hangars at the base, with their entrances singed by fire.

Syrian President Bashar al-Assad, shown speaking during an interview in Damascus on April 3, 2017, called the U.S. strikes on a Syrian military base “unjust and arrogant aggression.” (Sana Handout/European Pressphoto Agency)

But by nightfall, the Syrian Observatory for Human Rights reported that two jets had left the air base to bomb Islamic State positions. The Pentagon could not confirm the reports, but said it would have no reason to doubt reporting from the region.

Talal al-Barazi, the governor of Homs province, where the air base is located, said in a phone interview that the attack would not cause the Syrian government to change course in the war. 

“The war on terrorism is sustained, and the protection of the people is our priority,” he said. He asserted that the U.S. strike was aimed at weakening the Syrian army and allowing the Islamic State to launch attacks on areas near the air base. 

In unusually forceful comments, Assad called the U.S. strike “unjust and arrogant aggression” that would only increase his government’s determination to “crush” militant groups in Syria, according to the state news agency.  

But Assad’s opponents appeared to scent vulnerability in the Syrian leader for the first time since Russia’s 2015 military intervention turned the tide of the war in the government’s favor.

“God bless Trump, but the story does not end here,” said Bayan al-Qalamumni, a former civil servant from the Damascus suburbs now living as a refu­gee in southern Turkey. 

Mahmoud al-Hadi, a spokesman for the U.S.-allied Raqqa Revolutionaries Brigade, said the strike was welcome but “not sufficient.” The Syrian air force, he added, “should be neutralized completely, and Syrian rebels should exploit the chance of international community support to unite themselves against the regime, and terrorist and extremist groups as well.”

The Syrian government has denied responsibility for the chemical attack, insisting it would never use chemical weapons. That claim is now likely to be subjected to a fresh round of scrutiny. The Organization for the Prohibition of Chemical Weapons, a global watchdog, said Thursday that it had initiated contact with Assad’s government and that it was investigating reports that the attack likely involved sarin, a nerve agent so deadly that it can kill in minutes.

The U.S. military operation might deter the use of chemical weapons in future attacks, experts said, but it is unlikely to shift the balance of power in a war that Assad’s military has all but won. 

At the very least, though, Assad may now face increased pressure to return to a peace process that has repeatedly broken down. Despite its strong public defense of the Syrian government’s actions, Moscow is now fashioning itself in the role of peacemaker, overseeing a stuttering set of negotiations between rebel groups and Assad’s government in the Kazakh capital, Astana. 

“The most significant consequence of these strikes will be to push Russia to apply more pressure on the regime to join the peace talks in Astana,” said Hilal Khashan, a professor at the American University of Beirut. “Russia is committed to that process now, so they have to make it work.”

Suzan Haidamous in Beirut and Thomas Gibbons-Neff in Washington contributed to this report.