Two Russian air force planes landed in Venezuela's main airport on Saturday carrying a Russian defense official and nearly 100 troops, according to a local journalist, amid strengthening ties between Caracas and Moscow.

A flight-tracking website showed that two planes left from a Russian military airport bound for Caracas on Friday, and another flight-tracking site showed that one plane left Caracas on Sunday.

The report comes three months after the two nations held military exercises on Venezuelan soil that President Nicolas Maduro called a sign of strengthening relations, but which Washington, who has backed an attempt to seize power by opposition leader Juan Guaido, criticized as Russian encroachment in the region.

Reporter Javier Mayorca wrote on Twitter on Saturday that the first plane carried Vasily Tonkoshkurov, chief of staff of the ground forces, adding that the second was a cargo plane carrying 35 tons of material.

An Ilyushin IL-62 passenger jet and an Antonov AN-124 military cargo plane left for Caracas on Friday from Russian military airport Chkalovsky, stopping along the way in Syria, according to flight-tracking website Flightradar24.

The cargo plane left Caracas on Sunday afternoon, according to Adsbexchange, another flight-tracking site.

The flights carried officials who arrived to "exchange consultations," wrote Russian government-owned news agency Sputnik, which quoted an unnamed source at the Russian embassy.

"Russia has various contracts that are in the process of being fulfilled, contracts of a technical military character," Sputnik quoted the source as saying.

A Reuters witness saw what appeared to be the passenger jet at the Maiquetia airport on Sunday.

It was not immediately evident why the planes had come to Venezuela.

Venezuela's Information Ministry did not immediately reply to a request for comment.

Russia's Defense Ministry and Foreign Ministry did not reply to messages seeking a comment. The Kremlin spokesman also did not reply to a request for comment.

The Trump administration has levied crippling sanctions on the OPEC nation's oil industry in efforts to push Maduro from power and has called on Venezuelan military leaders to abandon him. Maduro has denounced the sanctions as U.S. interventionism and has won diplomatic backing from Russia and China.

In December, two Russian strategic bomber aircraft capable of carrying nuclear weapons landed Venezuela in a show of support for Maduro's socialist government that infuriated Washington.

Maduro on Wednesday said Russia would send medicine "next week" to Venezuela, without describing how it would arrive, adding that Moscow in February had sent some 300 tonnes of humanitarian aid.

Venezuela in February had blocked a convoy carrying humanitarian aid for the crisis-stricken country that was coordinated with Guaido's team, including supplies provided by the United States, from entering via the border with Colombia.