The White House said Tuesday that Russia's Wagner mercenary group plans to provide an air defence system to Lebanon's Hezbollah militants or to the regime in Tehran, as part of an "unprecedented defense cooperation" between the two US adversaries.

"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 told reporters.

The Wall Street Journal, quoting unidentified US officials, said earlier this month that Wagner was preparing to supply the Pantsir-S1, a Russian self-propelled anti-aircraft gun and missile system known as SA-22 by NATO.

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.

He added that Iran was "considering providing Russia with ballistic missiles now for use in Ukraine in return for that support."

Washington has been warning of deepening military relations between Moscow and Tehran -- a burgeoning relationship that Kirby described as "obviously harmful to Ukraine, certainly harmful to Iran's neighbors, quite frankly harmful to the international community."

Russian Defense Minister Sergei Choigou paid an official visit to Iran in September, described as an "important step" for military cooperation between the allies.

Both countries are subject to international trade sanctions and have forged close ties in a number of sectors.