Russia sent two planes with dozens of soldiers and military advisers to Venezuela’s capital of Caracas over the weekend amid growing tensions in the South American country, an anonymous Venezuelan official has said.

Venezuela’s political crisis escalated on Sunday when opposition leader Juan Guaido, who declared himself interim president in January, called on his supporters to prepare to take power in the country. Moscow, which backs President Nicolas Maduro’s government, has previously said it would not allow a U.S.-backed color revolution in the country.

Russian military officials arrived in Caracas to discuss strategy, equipment maintenance and training, an unnamed Venezuelan official told The Associated Press Monday.

The Chief of Staff of Russia’s Ground Forces Vasily Tonkoshkurov, nearly 100 troops and 35 metric tons of equipment were on board the planes, media reports said. 

The flights also carried officials who arrived to “exchange consultations,” the state-funded Sputnik news agency reported, quoting 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 cited the source as saying.

Flight-tracking data showed that an Ilyushin IL-62 passenger jet and an Antonov AN-124 military cargo plane left from Russia for Caracas on Friday.

The planes landed three months after the two nations held military exercises in Venezuela that President Nicolas Maduro called a sign of strengthening relations, but which Washington criticized as Russian encroachment in the region.

High-level U.S.-Russian talks on how to defuse Venezuela’s crisis ended early last week with the two sides still at odds over the legitimacy of Maduro.

Reuters contributed reporting to this article.