Hillary Clinton's campaign accused Donald Trump of "troubling connections" to the Kremlin after Paul Manafort, his key aide, was forced to deny allegations that he received millions of dollars in cash payments from pro-Russian politicians in Ukraine.

Handwritten entries in a secret ledger unearthed by Ukraine’s National Anti-Corruption Bureau showed Viktor Yanukovych, the country's pro-Russian former president, earmarked $12.7 million (£9.8 million) for Mr Manafort between 2007 and 2012, the New York Times reported.

Mr Manafort was working for Mr Yanukovych's party as a political consultant.

Investigators are looking into whether it was part of an illegal, off the-books scheme. Mr Manafort, the Republican presidential nominee's campaign manager, vehemently denied any wrongdoing, saying he had never received the payments.

It was another setback as the billionaire, trailing in polls, attempted to present himself as a candidate with serious policies.