The Syrian base hit by US missile strikes has played a central part in the war, housing a jet fleet responsible for extensive bombing of the north and large numbers of Hezbollah and Iranian fighters who had turned the conflict in Bashar al-Assad’s favour.



All Syrian forces had evacuated the al-Shayrat airfield by the time the strikes occurred, as had fighters from the Lebanese militia, who had been heavily involved in countering an opposition offensive on nearby Hama in recent weeks.

Sources in Beirut said no Hezbollah members had been killed in the attack and some senior Syrian officers had sent their families to Beirut, anticipating further clashes. But politicians allied with Hezbollah said they were not expecting further US involvement, or an escalation of tensions between Washington and Assad’s two main backers, Russia and Iran.

Senior members of Syria’s armed opposition said between 14 and 20 ageing Sukhoi jets had been destroyed in the base – roughly 10% of the Syrian air fleet. Its two runways were damaged, as were storage sites, a weapons dump and an air defence system.

But the damage to the runways appears not to have put the base out of action: by Friday, government warplanes were once again reported to have taken off from the runway.

Up to six people, believed to be civilians, were killed outside the base by shrapnel that flew up to 500 metres, an opposition member said.



Iranian forces had been housed in a nearby hotel in recent months, but they too were evacuated on Thursday night.



The Pentagon believes that Russian officers were present inside the sprawling site when a sarin-filled shell was loaded on to one of the Sukhoi jets on the night of 3 April. US intelligence officials have not established, however, whether the Russians knew that the process was happening, or had specific knowledge of the attack.



A visual guide to the US missile strikes on a Syrian airbase Read more

US military officials also released what they said was a flight path taken by the jet that launched the attack at 6.30am the following morning, which plotted it taking off from the base, then returning to it after manoeuvring over the town of Khan Sheikhun, where more than 70 people were killed in Tuesday’s gas attack.



Washington used an established channel with Russian commanders to warn of the upcoming strike, which the Russians then relayed to their hosts. Strike planners did not anticipate casualties among Assad’s forces, nor decisive damage to the regime’s air fleet.



Instead, the bombing was tailored to strike a symbolic blow at the heart of one of Assad’s most strategic bases, which has featured heavily in allegations of chemical use. Western intelligence officials believe the same base was used to launch a sarin attack in eastern Hama in early December, where up to 93 people were killed and more than 300 others suffered the same symptoms as the survivors of the attack on Khan Sheikhun.

The small town is at the first major junction on the highway north of Hama. Further north lies the city of Idlib, from where the opposition launched an extensive attack on Hama in mid March. Officials in Beirut believe the sarin attack may have been launched both to avenge the Hama offensive and to clear a way for an eventual regime push towards Idlib.

'The dead were wherever you looked': inside Syrian town after chemical attack Read more

The Guardian visited Khan Sheikhun on Thursday and saw the impact point of the shell that contained sarin – a hole on a road metres away from where dozens of those who died in the attack had been asleep in their homes.



Buildings near the site had not been damaged by recent air strikes, directly contradicting Russia’s claims that a jihadist weapons depot had been hit, causing a release of sarin claimed to have been stored there. The Guardian inspected all surrounding commercial buildings. All contained small stores of agricultural goods; none of the sites had been contaminated.

Khan Sheikhun was again bombed on Friday by jets, believed to be Syrian. One senior western official said the decision to launch the strike had likely been driven by local battlefield dynamics, rather than regional political considerations.

“This is vengeance for the regime for what happened in Hama,” the official said. “This is them saying that they are the most ruthless force in the game, that they will hit 10 times harder than anyone who hits them. It is also about trying to open up a path to Idlib, for the eventual ground attack there.

“But they badly miscalculated. Somebody didn’t work out that it would be easy to get samples to the border to prove what happened. This was never going to remain shrouded in mystery.”



Another opposition supporter, who had been extensively involved in arming the opposition earlier in the war, said: “[The regime] are really quite old school. They have not evolved in their thinking at all. This is about projection of power to them. The more brutal, the better. Anything to incite fear. Obama was never speaking their language by trying to negotiate. They will never negotiate in good faith.”

Officials in Beirut and Turkey said there was little risk of an escalation and that the “free hand” that Assad had perceived he had no longer applied after the US strike.

“That’s the best we can hope for,” said an Ankara-based diplomat. “He will have to think very carefully about what he does from here. He is dealing with an unpredictable and volatile US president. That in itself removes the impunity.”

