"Our information... indicates that Wagner, at the direction of the Russian government, was preparing to provide an air defense capability to either Hezbollah or Iran," National Security Council spokesman John Kirby was quoted as having told reporters.
Earlier this month, The Wall Street Journal reported that the Wagner Group was preparing to supply the Pantsir-S1, a Russian self-propelled anti-aircraft gun and missile system known as SA-22 by NATO.
CNN later reported that the US has intelligence that Syrian President Bashar Al-Assad has agreed to provide Hezbollah with a Russian-made missile defense system.
Wagner, which is funded by the Kremlin, has been brought back in to line after a failed mutiny in June that presented the biggest threat to President Vladimir Putin's two-decade rule.
"We are certainly prepared to use our counterterrorism sanctions authorities against Russian individuals or entities that might make these destabilizing transfers," Kirby said on Tuesday, according to AFP.
He added that Iran was "considering providing Russia with ballistic missiles now for use in Ukraine in return for that support."
The US has previously warned that Iran had provided Russia with drones for use in its war against Ukraine.
In June, a US intelligence finding said that Iran is providing Russia with materials to build a drone manufacturing plant east of Moscow as the Kremlin looks to lock in a steady supply of weaponry for its ongoing invasion of Ukraine.