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.
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.
Who is affected by the sanctions?
China’s Equipment Development Department (EDD) and its head, Li Shangfu, are sanctioned for completing “significant transactions” with Russia’s state arms exporter, Rosoboronexport.
The EDD and Mr Li have been added to a Blocked Persons List, meaning any assets they hold in the US are frozen and Americans are “generally prohibited” from doing business with them.
Furthermore, the EDD is denied export licences and excluded from the American financial system.
Washington also blacklisted an additional 33 people and entities associated with Russian military and intelligence.
What US law governs the sanctions on China?
The Countering America’s Adversaries Through Sanctions Act (Caatsa) was passed in 2017 to provide the Trump administration with the necessary means to target Russia, Iran and North Korea with economic and political sanctions.
US President Donald Trump issued an executive order on Thursday intended to allow the sanctions to be implemented.
“The ultimate target of these sanctions is Russia,” a senior administration official told journalists.
“Caatsa sanctions in this context are not intended to undermine the defence capabilities of any particular country” but are “aimed at imposing costs on Russia in response to its malign activities”.
Similar action against other countries would be considered, Washington added.
How has Russia reacted?
A politician in Moscow said the US sanctions would have no impact on the sales of its fighter jets and missiles.
“I am sure that these contracts will be executed in line with the schedule,” Franz Klintsevich, a Russian member of parliament, was quoted as saying by Russia’s Interfax news agency.
“The possession of this of this military equipment is very important for China,” he added.
Asia is the most important foreign market for Russian arms producers, reportedly accounting for 70% of their exports since 2000.
India, China and Vietnam are the principal sources of demand for Russian weapons in the region, according to a recent Chatham House report.