The Russian government has denied that it has sent mercenaries to protect the Venezuelan president, Nicolás Maduro, after an opposition leader with backing from the United States declared himself the country’s president.

Russia has thrown its diplomatic weight behind Maduro in recent days, criticising the US for violating Venezuela’s sovereignty by supporting the leadership claim of opposition leader Juan Guaidó.

Reports emerged earlier this week that dozens or hundreds of Russian mercenaries, who have been active in Ukraine and Syria, had been sent to protect Maduro from a possible coup attempt. The move would suggest that Russia was willing to raise the stakes to protect its investment in its closest ally in the western hemisphere.

On a political news show on Sunday, Kremlin spokesman Dmitry Peskov denied that Russia had sent military personnel to the country. “Fear has a hundred eyes,” he said. He did not make a direct denial, however, because private military contractors do not work for the government.

Russia has spent billions to build up its influence in Venezuela and there are concerns that regime change could erase that investment.

The country has invested an estimated $17bn (£13bn) in cash-strapped South American nation, much of that in loans. In 2017, Russia agreed to restructure more than $3bn of Venezuelan debt and the Russian oil giant Rosneft has loaned a similar amount to PDVSA, the state-owned oil company. Rosneft also holds shares in Venezuelan oil production.

Another $3bn loan from Russia was used to buy weapons, including assault rifles, warplanes and helicopters, making Venezuela the largest operator of Russian military equipment in South America. Kalashnikov, the maker of the AK47, is building a factory in Venezuela, although its opening has been repeatedly delayed.

Estimates of how much Russia has invested in Venezuela vary. David Rozental, a researcher from the Institute of Latin America at the Russian Academy of Sciences, estimated the amount to be more than $20bn.

Vladimir Davydov, the academic director at the Institute of Latin America, said that Russia views Venezuela as its beachhead in Latin America and that the country’s large oil reserves made it a top priority for Russia. “What role will Russia play in the control of strategic resources? That is what is being decided in Venezuela,” Davydov said.

The man leading the charge has been Igor Sechin, the former military translator who now heads the Russian oil firm Rosneft. A fluent Spanish speaker, Sechin has met with Maduro regularly and has increased the Rosneft’s investment in Venezuelan oil production and its state-owned producer.

“[Sechin] knows Latin America quite well, he is very influential,” said Davydov. “He wants to maintain Rosneft’s position in Venezuela and there are different ways to do that.”

For now, Davydov and his colleagues said they did not expect Russia to involve itself militarily in the Venezuelan crisis, even in the event of American-backed intervention.

It would primarily seek a role as an intermediary, they said, as a means to project Russian power and to protect its investment.

Even in the case of a transfer of power, Russia may not stand to lose everything. “We didn’t conclude deals with [Hugo] Chávez or Maduro, we concluded deals with the parliament of Venezuela,” said Rozental, during a radio broadcast on Vesti FM this week. “In this sense, I don’t think that there’s a serious threat to Russian assets.”