It says such purchases contravene US sanctions on Moscow introduced in response to Russian actions in Ukraine and alleged inference in US politics.
China recently bought 10 Russian Sukhoi Su-35 fighter jets and S-400 missiles.
Beijing has not joined in the sanctions imposed on Moscow by the US and its Western allies since 2014.
Its forces took part in giant Russian war games held earlier this month.
Relations between the US and Russia deteriorated rapidly after Moscow annexed Crimea from Ukraine in 2014.
Russia's alleged meddling in the 2016 American presidential election and military involvement in Syria's ongoing civil war increased tensions.