WASHINGTON (AFP) - Donald Trump had a dream of building a golden 100-story tower overlooking the Kremlin in Moscow, the crowning achievement of his global real estate empire.

"Russia is one of the hottest places in the world for investment," he said in 2007.

"We will be in Moscow at some point."

But his pursuit of the Trump Tower logo gleaming over the Russian capital now threatens his presidency.

On Thursday (Nov 29), his former lawyer Michael Cohen admitted in a court filing that they pursued the project throughout the first half of 2016 via contacts with Russian President Vladimir Putin's office, even after the real estate tycoon had captured the Republican nomination for the US presidency.

Felix Sater, another Trump associate who worked with Cohen on the project, told Buzzfeed and other media that they even planned to gift the US$50 million (S$69 million) penthouse to Putin - who is now accused by US intelligence of helping Trump win the 2016 election.

"All the oligarchs would line up to live in the same building as Putin," Sater said.

Cohen's admission contradicted previous claims he, Trump and Trump's family made that they had no business relations with Russia at the time.

Trump on Thursday branded his one-time top assistant an outright liar.

Still, the billionaire added, pursuing a deal with Russians during the 2016 presidential race wasn't illegal.

"There was a good chance that I wouldn't have won, in which case I would have gotten back into the business, and why should I lose lots of opportunities?" Trump said.

30-year Moscow dream

Trump was already one of the titans of New York real estate, known for his gold-trimmed flagship Trump Tower on Fifth Avenue, when he got the Moscow bug in 1986 in a lunch with Soviet ambassador Yuri Dubinin.

"Dubinin's daughter, it turned out, had read about Trump Tower and knew all about it," Trump recalled in his book The Art of the Deal.

"One thing led to another and now I'm talking about building a large luxury hotel, across the street from the Kremlin."

He travelled with then-wife Ivana to view potential sites the following year.

"It was an extraordinary experience," he wrote. "I was impressed with the ambition of the Soviet officials to make a deal."

The tycoon was bogged down over the next decade by multiple bankruptcies in his Atlantic City casinos.

By 1997, he was back at the idea, discussing a possible casino project with rising political star General Alexander Lebed.

He knew there was money and appreciation of his name: he was already selling Trump-branded condominiums in Florida to rich Russians.

'I really like Putin'

In the mid-2000s, Trump's son Donald Jr. made a half-dozen trips to Russia. One idea was to renovate an old Moscow hotel and rebrand it in the name of Trump's daughter Ivanka, who was creating her own line of jewellery.

Yet Russia was hard, Donald Jr. said in a 2008 speech.

"As much as we want to take our business over there, Russia is just a different world ... It is a question of who knows who, whose brother is paying off who. ... It really is a scary place."

Still, with the help of Russia-born Sater, they kept pushing, and Trump was enamored with Russia's strongman leader.

"I really like Vladimir Putin. I respect him. He does his work well. Much better than our Bush," he told Russian journalists.

The US financial crisis then intervened. But by 2013 Trump was back, taking his Miss Universe pageant to Moscow where he would try to advance new property projects.

His partner in the pageant was Moscow mall developer Aras Agalarov, then launching into the massive riverside Crocus City development.

"TRUMP TOWER-MOSCOW is next," Trump tweeted after the show.

By then Trump was already seriously mulling a White House run. He didn't put his Russia plans on hold for it.

"The Russian market is attracted to me," he told the US magazine Real Estate weekly about his 2013 visit.

"I have a great relationship with many Russians, and almost all of the oligarchs were in the room."

Former spy was Moscow intermediary

Court filings Thursday show that Cohen and Sater avidly pursued a new project through early 2016, with their eyes on well-connected partners and Russian bankers. Their main intermediary for contacts, according to Buzzfeed, was a former senior Russian military intelligence officer.

The court filings said Cohen kept Trump and his children up-to-date on the project.

In May 2016 Sater passed on to Cohen an invitation to attend a Russian economic forum the next month from a top Putin aide.

"The entire business class of Russia will be there as well," Sater wrote.

But Cohen never went.

On Friday Trump continued to play it all down, saying the Cohen admission was part of a political "witch hunt" against him.

"Against all odds, I decide to run for President & continue to run my business-very legal & very cool, talked about it on the campaign trail," he tweeted.

"Lightly looked at doing a building somewhere in Russia. Put up zero money, zero guarantees and didn't do the project."