Former U.S. Vice President Joe Biden, a frontrunner for the 2020 Democratic presidential nomination, has said U.S. President Donald Trump in his conversation with Ukrainian President Volodymyr Zelensky "put personal politics above" presidential oath.

"Our president put personal politics above his sacred oath. The House must do its job and hold Donald Trump to account for his abuse of power. I will do mine, making my case for a presidency that will mean real help for those in our country who need it most," Biden wrote on Twitter on September 25.

Read alsoZelensky comments on July 25 call with Trump: "I think you read everything"

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As UNIAN reported, Zelensky's press service said on July 25 that during a telephone conversation, Trump expressed his conviction that the new Ukrainian authorities would be able to quickly improve Ukraine's image and "complete an investigation into corruption cases that had hindered interaction between Ukraine and the United States."

Trump's July 25 telephone call with Zelensky is at the center of an escalating battle over a whistleblower's complaint reportedly concerning the U.S. leader's dealings with Ukraine that the administration refused to give Congress.

The media suggested that during the conversation with Zelensky, Trump could have repeatedly insisted that Ukraine investigate the actions of influential politician from the U.S. Democratic Party and former U.S. Vice President Joe Biden.

Read alsoU.S. expects "much more honesty" in Ukraine – Trump

On September 21, U.S. congressmen called on the Trump administration to provide the transcript of his July 25 phone call with Zelensky.

On September 25, the White House published the transcript.

UNIAN memo. Ukrainian authorities have been probing into money laundering in the amount of over US$33 million during the acquisition of a group of companies of Kherson oil transshipment, in which Wirelogic Technology AS, Digitex Organization LLP, and ex-Minister of Ecology, businessman Mykola Zlochevsky's Burisma Holdings Limited were involved.

Hunter Biden, son of former U.S. Vice President Joe Biden, was a member of the latter's board.

On May 14, the then Prosecutor General, Yuriy Lutsenko, said that Ukraine was ready to transfer materials on Burisma to U.S. law enforcement agencies. According to him, the investigation had a printout of all Burisma payments, including to senior U.S. officials.

Yet, Lutsenko emphasized, the foreigners who were involved in the management of Burisma had not violated Ukrainian legislation.