(CNN) Ukrainian President Volodymyr Zelensky on Tuesday would not answer if it was his understanding that American military aid for Ukraine and an investigation into former Vice President Joe Biden and his son Hunter was linked.

When approached by CNN at the United Nations in New York, Zelensky simply responded that his conversations with President Donald Trump are "private and confidential."

Zelensky is at the center of a political storm in the United States after reports that Trump pressured him to investigate Hunter Biden, who sat on the board of Ukrainian gas company that was under investigation by Ukraine's general prosecutor while Joe Biden was vice president. There is no evidence of wrongdoing by either Joe or Hunter Biden.

Trump on Sunday acknowledged the phone call and that he discussed Biden, but he has denied doing anything improper. Trump tweeted Tuesday he has "authorized the release tomorrow of the complete, fully declassified and unredacted transcript of my phone conversation with President Zelensky of Ukraine."

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