Russian military officials have arrived in Venezuela to discuss equipment maintenance, training and strategy, officials from both countries have said.

Images released of nearly 100 Russian soldiers arriving in Venezuela have reignited speculation about the level of Moscow’s support for the country’s embattled president, Nicolás Maduro.

The explanations by officials for the visit came after a Russian-flagged cargo plane and an airliner were spotted at Maiquetía airport outside Caracas guarded by a contingent of Venezuelan national guardsmen.

A Venezuelan official said the aircraft arrived this weekend as part of ongoing military cooperation between the two allies. An unnamed Russian official told the state news agency RIA Novosti that there was “nothing mysterious” in the visit.

In a phone call with his Russian counterpart, the US secretary of state, Mike Pompeo, called on Russia to “cease its unconstructive behaviour” by supporting Maduro, the state department said on Monday.

The state department spokesman Robert Palladino said Pompeo had spoken to the Russian foreign minister, Sergei Lavrov, about Venezuela. “The secretary told Russian foreign minister Lavrov that the United States and regional countries will not stand idly by as Russia exacerbates tensions in Venezuela,” Palladino said in a statement that also condemned Russian military support for the “illegitimate regime of Nicolás Maduro”.

Photographs of the planes attracted attention after news reports in January that Russian mercenaries had flown to the country to protect Maduro. Russia’s military has been accused of using its aircraft to provide logistics for private military companies, in particular for Wagner Group paramilitaries active in Syria.

Venezuela was for years one of the largest importers of Russian military technology and has Russian warplanes, anti-aircraft missiles and other weapons systems that require maintenance and training, Russian military experts said. The cargo plane may have been carrying spare parts.

“It would be wrong to suggest this is some kind of major deployment,” one person close to the Russian defence ministry told the Guardian.

Flightradar24, a flight-tracking site, showed the flight path on Saturday of what it listed as a Russian air force plane, apparently headed to Caracas while flying across the Caribbean.

Javier Mayorca, a Venezuelan journalist, tweeted that a Russian cargo plane with military equipment also arrived in Caracas on Saturday.

Before Monday, both planes, an Il-62 and an An-124, had made regular trips from a Moscow military airport to a Russian airbase in Syria.

Mayorca said about 100 Russian soldiers led by Gen Vasily Tonkoshkurov, head of the mobilisation directorate of Russia’s armed forces, disembarked along with about 35 tons of equipment.

A picture of a Russian-flagged aircraft posted on social media showed men in uniform clustered around it on the tarmac.

More Russian soldiers unload in #Venezuela to help prop up Pres. #Maduro. The Ilyushin IL-62M is used to carry military personnel and frequently flies troops from #Russia to Syria -- indeed it stopped in #Syria on its way from Russia to #Caracas. pic.twitter.com/YfU2SnZacJ — Prof. Steve Hanke (@steve_hanke) March 24, 2019

Russia backs Maduro, who has rejected demands from the US and dozens of other countries that he resign.

Russia and China are the main allies of Venezuela. Both have lent billions of dollars to the oil-rich South American country, propping up Maduro’s anti-US government.

Russia has also vocally opposed US moves to sanction Maduro and his government, and to recognise the opposition leader, Juan Guaidó, as Venezuela’s interim president.

US moves against Caracas have ratcheted up in recent weeks, with Donald Trump warning “all options” – implicitly including US military intervention – were being considered.

On 28 April, US sanctions are set to escalate with a ban on crude oil imports from Venezuela. The US is historically Venezuela’s biggest oil buyer, and that step is expected to severely crimp the Maduro government’s already diminished finances.

Russia has previously signalled its support for Maduro by sending two TU-160 bombers to Venezuela last December to take part in a military exercise.

Russia’s president, Vladimir Putin, has a record of ordering his military – or paramilitary – forces into several theatres to challenge US strategies, notably in Syria and Ukraine.

Some Kremlin critics expressed concern that Russia could be planning to establish a base in Venezuela. Military experts said the airlift to begin preparations for a base would have to be far larger.

Any Russian foothold in Latin America, especially Venezuela, would alarm the US military. It would also be a political test for Trump, who has routinely avoided criticising Putin.