A Ukrainian oligarch paid $150,000 to the Trump Foundation in exchange for Donald Trump making a speech at one of his conferences, it has emerged.

Tax returns for 2015 released by the Trump Foundation show the UK office of Victor Pinchuk's foundation made the substantial payment that year. The billionaire has also given millions to The Clinton Foundation.

Pinchuk's foundation confirmed to Buzzfeed that the money was given in exchange for Trump's video-like speech in 2015 - leaving Trump open to similar questions about donors and conflicts of interest that plagued Hillary Clinton's presidential run.

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Donor: The foundation of Ukrainian billionaire Victor Pinchuk paid $150,000 to the Trump Foundation in 2015, Trump's tax returns show. In return, Trump spoke at his conference

Talk: Trump talked by video (pictured) at Pinchuk's 2015 conference in Ukraine. He said the US needed to take a hard line with Putin - in contrast with his stump speeches at US rallies

'The payment to President-elect Trump’s foundation was in support of video link appearance at a conference called Yalta European Strategy Annual Meeting, which the Victor Pinchuk Foundation and Yalta European Strategy [YES] - an NGO founded by Mr Pinchuk - organize annually in September in Ukraine,' Thomas Weihe, head of the board of the Pinchuk Foundation, wrote.

He added: 'Mr Pinchuk had met Mr Trump some years ago in New York, this is how the invitation for Mr Trump to speak at the [Kiev] meeting came about.'

Pinchuk runs investment advisory company EastOne and is one of Ukraine's richest men, with $1.52billion to his name as of last year.

His foundation had donated at least $8.6million to the Clinton Foundation when Hillary Clinton was Secretary of State.

Clinton's decision to host him at a dinner during that time led to questions being raised during her presidential run in August, The Wall Street Journal reported.

Now Trump may be subjected to the same kinds of questions about his business and charitable interests, and whether they conflict with his role as President.

Some of those questions won't be able to be answered until after he is in office, however - his 2016 tax returns will probably not be filed until November 2017.

Questions: Pinchuk also gave $6.8m to the Clinton Foundation. Questions were asked in August after it emerged she had hosted him for dinner while Secretary of State

YES's stated aim is 'to develop strategies for Ukraine and Wider Europe and promote Ukraine’s European integration'.

It is pro-Western and opposes Vladimir Putin's expansionist attitude towards former Soviet states.

Despite stump speeches to supporters suggesting a warmer relationship between the US and Russia, Trump's talk at the YES Annual Meeting promised a stronger line on Russian intervention in Ukraine.

'The United States has been supportive [toward Ukraine] but more verbally than anything else,' he said to applause from the audience.

'Our President is not strong and he is not doing what she should be doing for the Ukraine,' he continued, to shouts of 'Yeah! and louder applause.

'So far we have all lip service and in this country we call it just that - it's lip service and nothing else.'

He added that 'Part of the problem that Ukraine has with the United States is that [Russian President Vladimir] Putin does not respect our President whatsoever,' then expanded that thought to say the 'lack of respect' was a problem for the whole world.

Trump's remarks on the campaign trail about being more friendly to Russia have disturbed those who want to Ukraine to maintain its independence from Putin's influence.