The military presence "is regulated by an agreement" between Moscow and Caracas, said the foreign ministry. Opposition leader Juan Guaido has rejected the deployment, saying it violates the constitution.
Moscow is "developing cooperation with Venezuela in strict accordance with the constitution of that country and with full respect for its legal norms," said Foreign Ministry spokeswoman Maria Zakharova.
"The presence of Russian specialists on Venezuelan territory is regulated by an agreement between the Russian and Venezuelan governments on military and technical cooperation that was signed in May 2001."
Critics accused acting President Nicolas Maduro of sidelining the opposition-held National Assembly, arguing that the power to authorize foreign military missions in the country lie with the legislature.
"It seems (Maduro's government) doesn't trust its own troops, because it is importing others … once again violating the constitution," said Juan Guaido, who leads the opposition as interim president of Venezuela.
Maduro's government "didn't bring generators in those (Russian) planes, they didn't bring engineers," added Guaido, referring to the second nationwide blackout to hit Venezuela in a month. "No, they brought in foreign troops onto national soil."
In March 2017, violent protests erupted across the country in response to a Supreme Court decision to strip the legislative branch of its powers. Amid an international outcry, President Nicolas Maduro reversed the decision, but it was too late. Thousands continued to take to the streets, calling for new elections. More than 100 people were killed in clashes with security forces.
Image: Getty Images/AFP/J. Barreto
Hunger, a growing problem
The violence added to the ongoing economic and political crisis in Venezuela. Many Venezuelans spend more than 30 hours a week waiting in lines to shop, and are often confronted with empty shelves when they finally enter a store. President Maduro blames the crisis on US price speculation. The opposition, however, accuses the Socialist government of economic mismanagement.
Image: picture-alliance/AA/C. Becerra
Health care in crisis
The crisis has even affected health care in the oil-rich nation. Venezuelans often head to Colombia to collect medical supplies to send home, as seen in this picture. Hospitals across Venezuela have compared conditions to those seen only in war zones. As patient deaths rise, health officials have sounded the alarm on the rise of malaria and dengue fever.
Image: picture alliance/dpa/M.Duenas Castaneda
Power grab
By July 2017, Venezuela's pro-government Constituent Assembly was established. For observers, it had all the hallmarks of a power grab. The new body adopted the authority to pass legislation on a range of issues, effectively taking away the powers of Venezuela's elected congress, which was under the opposition's control. The move drew wide international condemnation.
Image: picture-alliance/dpa/P. Miraflores
The West sanctions
In response to the political crisis, the United States and European Union imposed a series of sanctions against ruling officials. The US blacklisted members of the Constituent Assembly and froze all of Maduro's assets that are subject to US jurisdiction. The EU banned arms sales to the country.
Image: picture-alliance/dpa/AFP/T. Schwarz
Government victorious in regional elections
In October 2017, Venezuela held two votes: regional elections and elections for governors, which were long overdue. The opposition boycotted the vote, but then split, as some candidates and small parties chose to participate. This caused a deep rift within Maduro's opponents. The government went on to sweep the vote, which detractors say was unfair and heavily favored the regime.
Image: picture-alliance/AP Photo/A. Cubillos
Debt default
In November 2017, the oil-rich, cash-poor nation faced its day of reckoning. Credit ratings agencies declared Venezuela and its state-run oil company in "selective default." But Russia offered to restructure the South American country's debt to ensure Caracas pays its other creditors. US and EU sanctions, however, limited the chance of an agreement.
Image: picture-alliance/AP Photo/A. Cubillos
Presidential elections scheduled
The National Assembly announced in January 2018 that it would grant Maduro's call for snap presidential elections. The electoral authority, CNE, held the elections on May 20. The EU, the US and 14 Latin American nations warned that they would not recognize the results. The mainstream MUD opposition alliance boycotted the vote, leaving only one possible outcome.
Image: Getty Images/AFP/F. Parra
Maduro wins ...
Maduro was re-elected to a second six-year term with about 68 percent of the vote. Turnout was only 46 percent, according to electoral authorities. However, the MUD opposition alliance put turnout at less than 30 percent. The Organization of American States (OAS) called the elections neither free nor fair.
Image: picture-alliance/AP Photo/A. Cubillos
... Guaido assumes power
But weeks into the new year, the situation took a drastic turn. On January 23, 2019, parliament president Juan Guaido declared himself interim president of Venezuela — a move that was quickly recognized by US President Donald Trump. Maduro called it a US-backed "coup." Days later, the US sanctioned Venezuela's state oil firm, while Guaido staked his claim on the country's foreign assets.
Image: Imago/Agencia EFE
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US 'determined to support Guaido'
In January, then-opposition lawmaker Guaido declared himself president of Venezuela in a stunning move that undermined Maduro's authority in the country.
Washington immediately recognized him as the legitimate president of the oil-rich, cash-strapped country. Shortly after, Germany and other Western countries recognized him. But Maduro's regime continues to enjoy support from countries such as Russia, China and Turkey.
Ahead of a meeting between Fabiana Rosales, Guaido's wife, and US Vice President Mike Pence at the White House on Wednesday, US President Donald Trump's administration reiterated its support for the opposition leader.
"The United States is determined to support Interim President Guaido's leadership as he champions freedom and the restoration of democracy for the Venezuelan people," said the White House in a statement.
Trump has repeatedly said that he will not "rule out" a military option when dealing with Maduro's regime. But Brazilian Defense Minister Fernando Azevedo e Silva said his country will not consider military force, adding that he believes a peaceful solution can be found.