A Russian deputy prime minister secretly met with oligarch Oleg Deripaska to discuss US relations after Paul Manafort reportedly offered Mr Deripaska briefings on the Trump campaign, according to videos discovered by a Russian opposition activist.

While a recorded snippet of Mr Deripaska's alleged conversation with Sergei Prikhodko, deputy prime minister and head of the government executive office, does not specifically mention Donald Trump, the fact of their meeting on a yacht raises further questions of collusion with Vladimir Putin's government.

The rendezvous at sea with Mr Prikhodko suggests a cosy relationship between Mr Deripaska, the president and largest shareholder of the aluminium giant Rusal, and the Russian government.

It reportedly took place in August 2016, a month after Mr Manafort, then Mr Trump's campaign manager, offered “private briefings” to Mr Deripaska, according to an email seen by The Atlantic.

Sergei Prikhodko, front left, attends a meeting with Vladimir Putin in 2006 credit: Sputnik/Alamy Stock Photo

The Telegraph could not independently confirm the validity of the recordings, and representatives for Mr Deripaska and Mr Prikhodko did not respond to phone calls and written requests for comment. The metals magnate has denied receiving briefings from the Trump campaign, although he admitted hiring Mr Manafort as a consultant in previous years.

MI6 has raised concerns that Mr Deripaska was able to hold a £1 billion London Stock Exchange offering in November, The Telegraph reported on Tuesday.

The oligarch is seen talking to a man who appears to be Mr Prikhodko in videos published in June on the Instagram account of Nastya Rybka, a model who has posted videos of herself embracing the aluminium tycoon. A caption said the two men were trying to “solve the issue with America”.

Paul Manafort stands between Donald and Ivanka Trump at the 2016 Republican Convention, where Mr Trump clinched the party's nomination for president credit: Brooks Kraft/Getty Images

Activist Alexei Navalny, who has been calling for an election boycott after he was barred from challenging Vladimir Putin for the presidency, revealed the videos in an online investigation. He claimed taking the deputy prime minister on a yacht with young women amounted to bribery.

Using Ms Rybka's photographs and open source documents to identify the yacht as the Elden, which is officially owned by Mr Deripaska's mother, Mr Navalny discovered through a tracking service that the ship had been cruising near Molde, Norway, in August 2016. The model posted photographs of the Norwegian coastline and herself on the yacht that same month.

Mr Navalny also said he found flight records showing that two private jets he has linked to Mr Deripaska flew to Molde in August 2016.

Ms Rybka, who appeared on a Russian state television show last year to explain her “man-hunting” techniques, described an August 2016 yacht trip in a book she wrote that year.

Nastya Rybka is seen with Mr Deripaska in the videos that showed his alleged meeting with Mr Prikhodko credit: Instagram

She transcribed the conversation from her video, naming the interlocutors as “Ruslan” and “Papa”. The meeting was so secret, Papa was taken off the yacht mid-voyage since “he couldn't even go onshore with Ruslan,” she wrote.

On Thursday, Ms Rybka posted a screenshot from Mr Navalny's video thanking him for his “concern” over her book's circulation.

“By the way, VVP has already read the book,” she wrote, referring to Vladimir Vladimirovich Putin by his commonly used initials.

Moscow police detain opposition leader Alexei Navalny last month at a rally calling for a boycott of March's presidential election credit: Evgeny Feldman/AP Photo

Mr Prikhodko has been a key Kremlin figure. A diplomat who became an aide to president Boris Yeltsin in 1997, he was in charge of foreign policy in Putin's first administration and served as a presidential aide until 2012.

Mr Deripaska hired Mr Manafort on a $10 million annual contract in 2006 after the Washington insider proposed a campaign to “greatly benefit the Putin government” by influencing US politics and media, Associated Press reported last year.

The oligarch denied this and filed a defamation suit that was thrown out by a judge in October.

He sued Mr Manafort in January for allegedly defrauding him of $18.9 million.

After publication of this article, a spokesperson for Mr Deripaska said in a statement that “outrageous false accusations appeared in social networks and mass media” and warned news outlets that he “will defend his honour and dignity in court”.