WASHINGTON (BLOOMBERG) - A company tied to a Russian oligarch sent US$500,000 (S$670,227.50) last year to an entity that lawyer Michael Cohen used to pay hush money to a porn actress who said she had a sexual encounter with President Donald Trump, according to attorney Michael Avenatti.

The bombshell revelations, which couldn't immediately be verified, caught companies and the President's team off guard.

It's the latest twist in litigation brought by Ms Stephanie Clifford, the porn actress known as Stormy Daniels, who was paid US$130,000 for her silence just before the 2016 presidential election.

Mr Avenatti, who represents Ms Clifford, said Mr Cohen submitted false information to First Republic Bank when opening a new account in October 2016.

Within 75 days, Mr Avenatti said, Mr Viktor Vekselberg - a Russian oligarch with links to Russian President Vladimir Putin - "caused substantial funds to be deposited into the bank account, from which Cohen made the payment" to Ms Daniels.

Special Counsel Robert Mueller's team has questioned Mr Vekselberg about the payments into Mr Cohen's account, CNN reported on Tuesday.

According to a tweet posted by a reporter, an attorney for Mr Cohen said he wouldn't discuss the US$500,000.

"I understand the shorthand you're using, but it wasn't a payment," the attorney, Mr Steve Ryan, told Ms Natasha Bertrand of the Atlantic.

Attempts were unsuccessful to reach Columbus Nova, the US investment vehicle for Mr Vekselberg's Renova Group that Mr Avenatti says made the payment. First Republic declined to comment.

Reached by telephone half an hour after Mr Avenatti posted the information, Trump attorney Rudy Giuliani said he doubted the report's veracity.

"I have no idea how he would know that. I have no reason to believe that anything he says is true," Mr Giuliani said.

"I consider him now (the) sort of a guy who books for Saturday Night Live. The guy is a pretty unsuccessful lawyer - can't remember a case he's ever had that meant anything - and I think he's desperate for money."

Mr Avenatti disclosed his information on Twitter without warning.

"Mr Trump and Mr Cohen have a lot of explaining to do," he wrote, adding a link to a site where the public could view a summary of his findings.

It's unclear whether Mr Avenatti obtained bank information, if it's accurate, as part of litigation involving Mr Trump, Mr Cohen and Ms Clifford over the non-disclosure agreement Mr Cohen negotiated.

Separately, federal prosecutors in Manhattan are investigating the payment and Mr Cohen's broader business practices.

Mr Avenatti named three companies, besides Columbus Nova, that he said transferred money into the account at First Republic.

Through January 2018, he said, Mr Cohen used the account for what Mr Avenatti called suspicious transactions totalling US$4.43 million.

The other companies were Novartis AG, AT&T and Korea Aerospace Industries Ltd.

The account belonged to Essential Solutions, a Delaware LLC that was established by Mr Cohen and has been previously identified as the source of the hush payment to Ms Clifford.

According to Mr Avenatti, Novartis made four payments of US$99,980 into the account in late 2017 and early 2018. Following the payments, totalling just under US$400,000, Mr Trump had a dinner meeting with Novartis's incoming CEO ahead of a World Economic Forum gathering in Davos, Mr Avenatti said.

A Novartis spokesman said he was looking into the issue.

Mr Avenatti cited four payments from AT&T of US$50,000 apiece, in late 2017, without further explanation.

AT&T announced just before the election that it would merge with Time Warner Inc. Mr Trump regularly criticised Time Warner's CNN unit on the campaign trail and threatened to derail any merger.

"Essential Consulting was one of several firms we engaged in early 2017 to provide insights into understanding the new administration. They did no legal or lobbying work for us, and the contract ended in December 2017," AT&T said in a statement.

Around that time, the Justice Department sued to block the merger. After a six-week trial, a judge is now weighing whether to approve the deal or block it.

Separately, Mr Avenatti cited a single payment of US$150,000 from Korea Aerospace. Representatives for the company couldn't immediately be reached for comment.

Although Mr Avenatti didn't offer an explanation for all the payments or the intended purposes of the funds, he also drew attention to what appeared to be Mr Cohen's personal accounts.

The longtime Trump lawyer opened two accounts at Morgan Stanley Smith Barney LLC and deposited three cheques totalling just over US$1 million that came from the Essential Consulting account, Mr Avenatti said.

Mr Avenatti said the transactions last summer appeared to have no "legitimate business purpose".

Mr Cohen has noted in court that Mr Trump was one of three legal clients he had last year, but that he had 10 other clients for whom he did unspecified business work.

Last month, the Trump administration imposed sanctions on Russians, including Mr Vekselberg and his Renova Group, that were intended to punish Russia for actions in Crimea, Ukraine and Syria, and for attempts to subvert Western democracies.

Mr Vekselberg, who founded Renova in 1990 and accumulated interests in Russia's oil, gas and aluminium industries, is Russia's fifth-richest person with a net worth of US$15.5 billion, according to the Bloomberg Billionaires Index.