US President Donald Trump's one-time campaign chairman secretly worked for a Russian billionaire to assist President Vladimir Putin, the Associated Press (AP) news agency reports.
Paul Manafort is said to have proposed a strategy to nullify anti-Russian opposition across former Soviet republics a decade ago.
AP says documents and interviews support its claims about Mr Manafort.
Mr Manafort has insisted that he never worked for Russian interests.
He worked as Mr Trump's unpaid campaign chairman from March until August last year, including the period during which the flamboyant New York billionaire clinched the Republican nomination.
He resigned after AP revealed that he had co-ordinated a secret Washington lobbying operation on behalf of Ukraine's ruling pro-Russian political party until 2014.
Newly obtained business records link Mr Manafort more directly to Mr Putin's interests in the region, AP says.
It comes as Trump campaign advisers are the subject of an FBI investigation and two congressional inquiries.
Investigators are reviewing whether the Trump campaign and its associates co-ordinated with Moscow to interfere in the 2016 presidential election campaign to damage Mr Trump's opponent, Hillary Clinton, a stern critic of Mr Putin.
Mr Manafort is said to have pitched the plans to aluminium magnate Oleg Deripaska, a close ally of President Putin.
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