REPUBLIKA.CO.ID, WASHINGTON -- Russia on Wednesday carried out its first airstrike in Syria, near the city of Homs, a US defense official said, marking the formal start of Moscow's military intervention in the 4.5-year-old conflict.

Speaking on condition of anonymity, the defense official said a Russian general working out of an intelligence center in Baghdad had walked over to the US embassy and given a verbal communique of the impending strike.

"They gave us a heads-up they were going to start striking in Syria," the official said, noting that the Russians gave about one hour's advance warning. "It was in the vicinity of Homs."

The strike came shortly after Russian President Vladimir Putin won unanimous support from parliament to carry out strikes in Syria.

The defense official said he was not aware of the impact of the strike or who was targeted.

Pentagon officials have described Russia's buildup of military hardware in the Latakia region in northwestern Syria and said Russia is making a forward operating base there.

So far, at least 500 troops as well as 28 fighter jets and several bombers and artillery units have been deployed to the base, US officials say.

The defense official said no action was necessary for coalition planes to avoid being in the same air space as Russian jets.

The Pentagon has repeatedly warned of the need for "deconfliction" to ensure coalition and Russian planes don't inadvertently cross paths.

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