Dozens of IS and al-Qaeda militants were reported killed in the raids, which Washington says had partly targeted extremists plotting an imminent attack against the West.
The operation carried crucial symbolic importance in the fight against Sunni IS as all five Arab nations involved in the airstrikes are Sunni-ruled.
The raids came after US and French air strikes in neighbouring Iraq, opening a new front in the war against the IS organisation.
Bombs over Syria
The bombings are being carried out using a number of means, including via F-22 Raptors.
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At a cost of around $160 million, they can reach speeds of up to 2,400 kmph while carrying up to 6 radar-guided missiles and 2 heat-seeking missiles.
Tomahawk missiles are also being used by US Navy surface ships, costing around $640,000 each.
There's also the MQ-9 Reaper drone, whose features include a multispectral targeting system with TV cameras, infrared sensor and laser illuminator.
At a cost of nearly $64 million, they can carry up to 4 laser-guided air-to-ground missiles.
