Donald Trump's personal lawyer, Michael Cohen, received a secret payment of at least $400,000 (£300,000) to fix talks between the Ukrainian president and President Trump, according to sources in Kiev close to those involved.
The payment was arranged by intermediaries acting for Ukraine's leader, Petro Poroshenko, the sources said, though Mr Cohen was not registered as a representative of Ukraine as required by US law.
The meeting at the White House was last June.
Shortly after the Ukrainian president returned home, his country's anti-corruption agency stopped its investigation into Trump's former campaign manager, Paul Manafort.
A high-ranking Ukrainian intelligence officer in Mr Poroshenko's administration described what happened before the visit to the White House.