"Their capabilities are largely the same, or almost identical, frankly," Baghdad-based military spokesman Colonel Steve Warren said.
"They continue to have air power there, they continue to have ground forces, they continue to have artillery. They still have Spetsnaz (special forces) providing advice and assistance to the Syrian regime."
Putin surprised the West in March when he ordered the "main part" of his forces to pull out of Syria, where Moscow has been conducting a bombing campaign to back up ally President Bashar al-Assad.
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Warren said Russian forces appeared to have established some sort of forward operating base near Palmyra, an ancient city whose Roman ruins were largely destroyed by Islamic State jihadists during the 10 months they held the town.
"Too early to tell whether or not they intend it to be a long term or short term venture," Warren said.
"They've established an operating base outside of Palmyra... And they're still building it up."
Warren said Russian forces had started to target IS fighters more actively, whereas their initial focus when they entered the fray last fall was on rebels opposed to Assad.