Guaido, who is recognized by the US and more than 50 countries as Venezuela's interim president, raised the issue in a speech to the National Assembly, which he heads.

"It seems (the government of President Nicolas Maduro) doesn't trust its own troops, because it is importing others ... once again violating the constitution," he said.

Russia, which recognizes Maduro as leader, on Saturday sent two planes carrying 100 troops and tons of military equipment to Venezuela.

Guaido said Maduro and his government "didn't bring generators in those (Russian) planes, they didn't bring engineers.... No. They brought in foreign troops onto national soil."

The opposition-controlled legislature, which has long been sidelined by Maduro, asserts that it alone has the legal power to authorize foreign military missions in Venezuela.

The Russian foreign ministry on Tuesday said the deployment was "in strict accordance with the constitution of that country and with full respect for its legal norms."

Russian Foreign Minister Sergei Lavrov has accused the US of trying to organize a "coup" in Venezuela, something Moscow has warned against.

US Secretary of State Mike Pompeo in return has warned that the US will not "stand idly by as Russia exacerbates tensions."

- Geopolitical tussle -

The geopolitical tussle between the former Cold War foes is playing out as Venezuela sinks deeper into economic and social crisis.

A near-nationwide blackout -- the second this month -- has gripped the country since Monday, deepening public frustration with conditions already marked by scarce food and medicine and runaway inflation.

Although US President Donald Trump has repeated that he is keeping "all options" on the table concerning Venezuela there have been no signs of imminent American military action in the oil-rich country.

Instead Maduro, who is deeply unpopular in Venezuela, retains power mainly through the loyalty of the military.

Guaido has been holding rallies for supporters around the country in which he has vowed to "very soon" take over the presidential palace. But so far Maduro has not been budged.

Russia remains Maduro's main ally. Moscow and Beijing, the country's top creditor, have lent the Maduro regime billions of dollars in exchange for a big slice of oil exports.