Two Russian military planes landed in Venezuela’s main airport on Saturday, reportedly carrying dozens of troops and large amounts of equipment.
The planes were sent to “fulfil technical military contracts”, Russia’s Sputnik news agency reported.
Javier Mayorca, a Venezuelan journalist, wrote on Twitter that he saw about 100 troops and 35 tonnes of equipment offloaded from the planes.
It comes three months after the two nations held joint military exercises.
Russia has long been an ally of Venezuela, lending the South American nation billions of dollars and backing its oil industry and military. Russia has also vocally opposed moves from the US to sanction the government of Venezuelan president Nicolás Maduro.
Mr Mayorca said on Twitter that a Russian air force Antonov-124 cargo plane and a smaller jet landed near Caracas on Saturday.
He said that Russian General Vasily Tonkoshkurov led the troops off one of the planes.
A military plane with a Russian flag on its fuselage could be seen on the tarmac at an airport on Sunday. Images on social media also appeared to show Russian troops gathered at the airport.
Ties between Moscow and Venezuela have strengthened in recent months, amid worsening relations between the US and Venezuela. In December, Russia sent two air force jets there as part of a military exercise.
Russia has condemned other foreign powers for backing Venezuelan opposition leader Juan Guaidó, who declared himself interim president in January.
President Maduro has accused Mr Guaidó of trying to mount a coup against him with the help of “US imperialists”.
The Kremlin echoed that line, accusing Mr Guaidó of an “illegal attempt to seize power” backed by the United States and pledging to do “everything required” to support Mr Maduro.
Mr Maduro narrowly won a presidential election in April 2013 after the death of his mentor, President Hugo Chávez. He was elected to a second term in May 2018 in an election which has been widely criticised by international observers.
Venezuela has experienced economic collapse, with severe food shortages and inflation reaching at least 800,000% last year.
Mr Guaidó has accused President Maduro of being unfit for office, and won the support of many in the country as well as US and EU leaders.
The Maduro government is becoming increasingly isolated as more and more countries blame it for the economic crisis, which has prompted more than three million people to leave Venezuela.
Meanwhile, Moscow has expanded co-operation with Caracas in recent years – increasing arms sales and extending credit.