Russian diplomats held secret talks in London last year with people close to Julian Assange to assess whether they could help him flee the UK, the Guardian has learned.

A tentative plan was devised that would have seen the WikiLeaks founder taken out of Ecuador’s London embassy in a diplomatic vehicle and transported to another country.

One ultimate destination, multiple sources have said, was Russia, where Assange would not be at risk of extradition to the US. The plan was abandoned after it was deemed too risky.

The operation to extract Assange was provisionally scheduled for Christmas Eve in 2017, one source claimed, and was linked to an unsuccessful attempt by Ecuador to give Assange formal diplomatic status.

The involvement of Russian officials in hatching what was described as a “basic” plan raises new questions about Assange’s ties to the Kremlin. The WikiLeaks editor is a key figure in the ongoing US criminal investigation into Russia’s attempts to sway the outcome of the 2016 presidential election.

Robert Mueller, the special counsel conducting the investigation, filed criminal charges in July against a dozen Russian GRU military intelligence officers who allegedly hacked Democratic party servers during the presidential campaign. The indictment claims the hackers sent emails that embarrassed Hillary Clinton to WikiLeaks. The circumstances of the handover are still under investigation.

According to Mueller, WikiLeaks published “over 50,000 documents” stolen by Russian spies. The first tranche arrived on 14 July 2016 as an encrypted attachment.

Assange has denied receiving the stolen emails from Russia.

Facebook Twitter Pinterest Assange emerges from the Ecuadorian embassy to address a crowd in May 2017. Photograph: Matthew Chattle/Barcroft Images

Details of the Assange escape plan are sketchy. Two sources familiar with the inner workings of the Ecuadorian embassy said that Fidel Narváez, a close confidant of Assange who until recently served as Ecuador’s London consul, served as a point of contact with Moscow.

In an interview with the Guardian, Narváez denied having been involved in discussions with Russia about extracting Assange from the embassy.

Narváez said he visited Russia’s embassy in Kensington twice this year as part of a group of “20-30 more diplomats from different countries”. These were “open-public meetings”, he said, that took place during the “UK-Russian crisis” – a reference to the aftermath of the novichok poisoning of Sergei and Yulia Skripal in March.

Sources said the plan involved giving Assange diplomatic documents so that Ecuador would be able to claim he enjoyed diplomatic immunity. As part of the operation, Assange was to be collected from the embassy in a diplomatic vehicle.

Four separate sources said the Kremlin was willing to offer support for the plan – including the possibility of allowing Assange to travel to Russia and live there. One of them said that an unidentified Russian businessman served as an intermediary in these discussions.

The possibility that Assange could travel to Ecuador by boat was also considered.

Narváez previously played a role in trying to secure Edward Snowden’s safe passage following his leak of secret NSA material in 2013. Narváez gave the former NSA contractor a so-called safe-conduct pass when he left Hong Kong for Moscow, where Snowden eventually found asylum. At the time, the then president of Ecuador, Rafael Correa, said Narváez had issued the pass without the government’s knowledge. The Spanish-language broadcaster Univision reported that Narváez travelled to Moscow the same day that he issued the safe passage document to Snowden; other sources have corroborated this report.

Assange’s Christmas Eve escape was aborted with just days to go, one source claimed. Rommy Vallejo, the head of Ecuador’s intelligence agency, allegedly travelled to the UK on or around 15 December 2017 to oversee the operation and left London when it was called off.

In February Vallejo quit his job and is believed to be in Nicaragua. He is under investigation for the alleged kidnapping in 2012 of a political rival to Correa.

Facebook Twitter Pinterest Ecuador’s president, Lenín Moreno, wants Assange to leave the country’s London embassy. Photograph: Mariana Bazo/Reuters

Ecuador’s new president, Lenín Moreno, has said he wants Assange to quit the embassy. In March the government in Quito cut off his internet access and restricted his visitors.

Melinda Taylor, a lawyer specialising in human rights and international criminal law who represents Assange, has denounced his confinement in the embassy.

“I think it is shocking that Assange has been detained arbitrarily for approximately eight years for publishing evidence of war crimes and human rights violations. The UK could end this situation today, by providing assurances that Assange will not be extradited to the United States.”

Sources offered conflicting accounts of who cancelled the Assange operation, but all agreed it was deemed to be too risky. The stumbling block was the UK’s refusal to grant Assange diplomatic protection.

Under UK law, diplomats are immune from criminal prosecution if their diplomatic credentials have been accepted by the British government, and if the Foreign Office has been alerted to the diplomat’s status.

This is not the first time Assange has apparently considered seeking refuge in Russia. The Associated Press reported this week that the WikiLeaks founder tried to obtain a Russian visa. He signed a letter in November 2010 granting power of attorney to “my friend” Israel Shamir – a controversial supporter who passed leaked US state department cables from Assange to journalists in Moscow. Shamir would deliver Assange’s passport to the Russian consulate, and collect it afterwards, Assange wrote.

At the time Assange was facing allegations of rape and sexual assault made by two women in Sweden. In 2012 he sought asylum in the Ecuadorian embassy after he lost a battle against extradition in the supreme court. Assange denies the women’s claims. Swedish authorities eventually dropped both cases after the statute of limitations expired. Assange faces arrest for breaching his bail conditions.

During the US presidential campaign, Donald Trump praised WikiLeaks for releasing the emails that damaged Clinton. Confidential visitor logs obtained by the Guardian reveal that Assange received several Russian nationals during the summer of 2016, including senior figures from RT, the Kremlin’s international propaganda channel.

In March 2017 WikiLeaks published confidential CIA documents. Assange believes a grand jury indicted him over this and other leaks, with the charges filed under seal. Were he to leave the embassy the US would seek his extradition, his lawyers say.

The Ecuadorian government declined to comment. The Russian embassy in London tweeted on Friday that the Guardian story was “another example of disinformation and fake news from the British media”.

• This article was amended on 20 December 2019 to omit the words “smuggle” and “plot” from the headline and text. They should have been avoided because they implied that diplomatic immunity is itself illicit. The Guardian’s independent standards Review Panel has issued a ruling on this article.