As Washington intensifies its push to drive Venezuela's President Nicolas Maduro from power, Russia's Vladimir Putin has vowed to support his South American "strategic partner" and warned of the "catastrophic" consequences if the United States were to send military assistance to opposition leader Juan Guaido.

When the US called a special United Nations Security Council session on Saturday, focused on the crisis in Venezuela, Russia used the session to warn against foreign intervention in the Latin American nation and accused the US of attempting a "coup".

Russian private military contractors have flown into Venezuela in recent days to increase security for Maduro, according to Reuters news agency.

Kremlin Spokesman Dmitry Peskov has denied the reports.

On Friday, Russia offered to mediate between Maduro's "legitimate" government and the opposition if necessary, saying it was ready to cooperate with all political forces that acted responsibly.

Moscow stands to lose a great deal if the Maduro government collapses, experts say.

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Pete Duncan, a Russian politics professor at University College London said: "Losing ties with Venezuela would be a huge blow to Russia. Putin will do his utmost to prevent regime change."

In the mid-1990s, Russia looked to Latin America for business opportunities.

Under Hugo Chavez - Maduro's predecessor - Russia became one of Venezuela's strongest allies with economic ties ranging from oil and loans to arms sales.

Duncan said that since Putin came to power in 2000, he has sought to cultivate partners in Latin America to counterbalance US influence in the region and to enhance Russia's great power status in the world.

Anton Barbashin, a political analyst at the Wilson Centre, said: "A major reason why Russia supports Maduro - the same principle why it supports [Syria's President Bashar] al-Assad - is the belief that no foreign power should meddle in the sovereign affairs of a particular state."

Vladimir Rouvinski, a foreign policy expert at Icesi University in Colombia, told Al Jazeera the Kremlin views Venezuela as the backyard of the US - in Washington's sphere of political influence - in the same way that Ukraine is in Russia's backyard - or what the Kremlin calls - "the near-abroad".

External observers typically view Cuba as Russia's key Latin American ally, but Rouvinski said Russia has never managed to restore the same level of confidence in Havana as in Soviet times.

The level of confidence between Moscow and Caracas is unrivalled.

"Venezuela is Russia's last asset in Latin America," said Rouvinski.

Russia's political elites believe the political developments that have occurred since the fall of the Soviet Union in 1991 - such as Georgia and Ukraine's efforts to achieve independence from Russia - are the result of US intervention.

"Russia wants to at least have a 'symbolic involvement' in Latin America as payback for US intervention in the near-abroad," said Rouvinski.

Putin found an ally in Venezuela. The late Chavez, and now Maduro have shared Putin's world view, opposed to US hegemony.

Ties between the US and Venezuela began to sharply deteriorate when the socialist President Chavez was elected in 1999.

Under the administration of then-President George HW Bush beginning in 2001, Chavez became highly critical of Washington's "imperialistic" foreign policy in the Middle East including the invasion of Iraq.

The US, meanwhile, has criticised the increasing authoritarian trends and human rights abuses in Venezuela.

In 2015, Caracas and Washington's relations hit rock bottom when former President Barack Obama issued an executive order, declaring Venezuela a "threat to US national security" and ordered sanctions against seven Venezuelan officials.

The US sanctions against Venezuela, which have intensified under President Donald Trump, prohibit US-based companies or people from buying and selling new debt issued by the state-run oil body, Petroleos de Venezuela (PDVSA) or the government.

'Economic warfare'

Former Special Rapporteur Alfred de Zayas, who visited Venezuela over a period of 21 years, has criticised the US sanctions, describing them as "economic warfare" that aims to strangle the economy and facilitate regime change.

Maduro's alliance with Russia has been important in strengthening a sense of sovereign Venezuelan national identity, in defiance of the US.

Caracas has historically taken a pro-Russian stance. Venezuela voted against the resolution condemning Russia's annexation the Ukrainian peninsula Crimea in 2014, and it was one of the few countries to formally recognise South Ossetia and Abkhazia, the regions of Georgia which broke away in 1991.

Since the annexation of Crimea and the resulting sanctions by the US, an increasingly isolated Russia has sought to strengthen its ties to Venezuela.

In recent years, Russia has become a "lender of last resort" of Venezuela's collapsing economy, destroyed by a drop in oil prices, hyperinflation and US sanctions.

In 2017, Reuters reported that the Russian government and Russia's largest state-owned oil company, Rosneft, advanced Venezuela at least $17bn in loans and credit lines between 2016 and 2017, becoming Venezuela's largest sponsor, after China.

PDVSA has been secretly negotiating with Russia since at least early 2018, offering Rosneft ownership interests in up to nine of Venezuela's most productive petroleum projects, according to Reuters.

Rosneft already has minority stakes in five joint projects with PDVSA, which produced 59 billion barrels of oil in 2017, more than eight percent of Venezuela's annual output.

Maduro also signed a deal giving Rosneft 49.9 percent of the US-based, Venezuelan-owned refiner Citgo as collateral for a $1.5bn loan to PDVSA.

Political significance

Rosneft's increasing influence in PDVSA helps to position Russia as a middleman in sales of Venezuelan oil to customers worldwide, including the US market.

The Russian fuel giant currently resells approximately 225,000 barrels per day of Venezuelan oil - about 13 percent of the nation's total exports, according to the PDVSA trade reports.

Since, as Rouvinski said, relations between Russia and Venezuela have been based on personal top-level diplomacy, a change in Venezuela's leadership threatens Rosneft's influence in Latin America.

Venezuela's opposition has also said, once in power, it will not honour Rosneft and PDVSA's joint ventures.

But Russia never expected to make tangible profits in Venezuela, according to Rouvinski.

The collapse of Maduro's government would have a far greater political significance than economic importance for Moscow.

"Without his [Putin's] support, the opposition would have a much easier time taking power," said Rouvinski.

As Venezuela's opposition gains strength and international backing, experts are certain that Putin will do whatever it takes to keep Maduro in power.

As Duncan said: "Russia has no reason to back down."