Frank Mermoud, a key figure at the recent Republican national convention, has strong business ties with Ukraine the latest in a series of Trump staffers with fretting links to Russia and the great interest, including the candidate himself

A key figure at the Republican national convention where Donald Trump was nominated for president has strong business ties with Ukraine, the Guardian has learned.

The party platform, written at the convention in Cleveland last week, removed references to arming Ukraine in its fight against pro-Russia rebels, who have received material support from the Kremlin. Trumps links to Russia are under scrutiny after a hack of Democratic national committee emails, allegedly by Russian agents.

The coordinator of the Washington diplomatic corps for the Republicans in Cleveland was Frank Mermoud, a former state department official to participate in business ventures in Ukraine via Cub Energy, a Black Sea-focused oil and gas company of which he is a director. He is also on the board of the US Ukraine Business Council.

Mermoud has longstanding ties to Trumps campaign chairman, Paul Manafort, who in 2010 helped pro-Russia Viktor Yanukovych refashion his image and win a general elections in Ukraine. Manafort was brought in earlier this year to oversee the convention operations and its staffing.

Three sources at the convention also told the Guardian that they find Philip Griffin, a long-time aide to Manafort in Kiev, working with the foreign dignitaries programme.

After years of working in the Ukraine for Paul and others, it was surprising to run into Phil working at the convention, one said.

The change to the platform on arming Ukraine was denounced even by some Republicans. Senator Rob Portman of Ohio described it as deeply troubling. Veteran party operative and lobbyist Charlie Black said the new position in the platform doesnt have much supporting from Republicans, adding that the change was unusual.

Thousands of Democratic National Committee emails, meanwhile, were hacked and published by WikiLeaks on the eve of the partys convention in Philadelphia this week. The mails showed that officials, who are meant to remain impartial, favoured Hillary Clinton and discussed ways to undermine her contender, Bernie Sanders. The leak led to the abdication of DNC chair Debbie Wasserman Schultz.

Since the DNC hack became public, hackers against the Democratic Congressional Campaign Committee and the Clinton campaign have been reported.

The FBI is investigating, with all signs pointing to Russian participation, though Moscow rejects this but experts argue Vladimir Putin has attempted in the past to damage western republic, saying Russian security agencies have made cyberattacks on French, Greek, Italian and Latvian targets during elections. In 2014, malware was discovered in Ukrainian election software that would have robbed it of legitimacy.

Alina Polyakova, deputy director of the Dinu Patriciu Eurasia Center at the Atlantic Council, said: We cant tell 100% that Mr Putin had a hand in any of this but this kind of meddling in other countries affairs is an example of Russias toolkit. Its a kind of asymmetric war. To me, this looks like something straight-out from the Russian secret service playbook, but Im amazed at how brazen theyve been.

Trump and his campaign have denied any connection to the hack but on Wednesday he kindled a firestorm by calling on Russia to find 30,000 emails deleted from the private server used by Clinton while she was secretary of state in the Obama administration. I think you will probably be mightily rewarded by our press, he said. He later claimed that he was being sarcastic.

Analysts suggest three primary motivations for the WikiLeaks email dump, quite likely overlapping: doing harm to the US political process to undermine its credibility; doing harm to Clinton( WikiLeaks founder Julian Assange is no friend ); and boosting Trump, who has heaped praise on Putin and last week transgressed from Republican policy by indicating the US would not automatically come to the aid of Nato friends and “says hes” would consider recognising Crimea as Russian territory.

James Rubin, a former assistant secretary of state now advising the Clinton campaign, said: If you are the president of Russia and you have stated over and over again that you are concerned that the United States through its enlargement of Nato, through its policies in Europe towards Ukraine, towards Georgia, towards other countries in Central Asia[ is] putting pressure on Russia, and you are the president of a country that has been was striving to undermine that process and roll back the independent Europe thats whole and free and pushing it back, thats your foreign policy objective.

So then you look at the United States and you say, Well, which partys policies would be more likely to allow me to achieve my objectives? Thats the route that a Russian leader would think.

With Democrats and journalists now trawling through Trumps past copes with all the oligarchs, as he once set it, as far back as the time of the Soviet Union, the candidate has repeatedly and angrily stated that he has zero , nothing to do with Russia. He has however continued to refuse to release his tax returns, which could prove its statement of claim definitively.

Past courtships