Two Russian military planes delivered troops and equipment to Venezuela over the weekend, Russian state news agency Sputnik reported Sunday.
The exchange was meant to “fulfill technical military contracts," the agency reported on the Spanish-language version of its website.
It gave no other details but quoted an unnamed official from the Russian embassy in Caracas saying "there is nothing mysterious" about the flights.
The Sputnik report was published after an independent Venezuela journalist, Javier Mayorca, said on his Twitter feed that a Russian air force Antonov-124 cargo plane and a smaller jet, apparently an Ilyushin Il-62, had landed at the main airport outside Caracas on Saturday. He said the planes offloaded around 100 Russian soldiers led by General Vasily Tonkoshkurov, head of the Mobilization Directorate of Russia's armed forces, and disembarked 35 tons of equipment.
Russia has also vocally opposed US moves to sanction Maduro and his government, and to recognize opposition leader Juan Guaido as Venezuela's interim president.
US moves against Caracas have ratcheted up in recent weeks, with President Donald Trump warning that "all options," implicitly including US military intervention, were being considered.
On April 28, US sanctions are to jump up a level with a ban on crude imports from Venezuela. Historically, the US has been Venezuela's biggest oil buyer, and the new sanctions are expected to severely crimp the Maduro government's already badly diminished finances.