State TV's website quoted the airspace division chief of Iran's Revolutionary Guard Gen Amir Ali Hajizadeh as saying "we had coordinated the fall of the engines in the desert in Iraq" in advance.
"The missiles we used were two-stage, it means that the engine separates from the warhead," said Hajizadeh.
Hajizadeh said US drones hovered over the targets after shortly the Iranian missiles hit them. He said the US may have been informed beforehand about the attack, as they had informed the Russian military, which may have relayed the information to the Americans.
He mocked media reports citing Israeli sources who said some of the missiles fell short of their targets, suggesting that the Israelis were unable to identify two-stage missiles, which are designed to split apart mid-flight.
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"Pity those who call themselves experts and do not understand that these were the first-stage engines (that fell), while the warheads hit targets."
Iranian reports said the guard launched six Zolfasghar and Qiam missiles. The latter have detachable warheads.
Iran says it is continuously developing its missile program; a key reason US President Donald Trump's administration has put Iran "on notice".
Iran has long supported Syrian President Bashar Assad in his fight against IS and other extremists groups.