The major interest United States president Donald Trump had in Ukraine was investigations into former vice president Joe Biden, a top US diplomat said.

Trump has been accused of trying to pressure Ukrainian President Vladimir Zelenski into investigating Biden but has denied any wrongdoing.

Bill Taylor, the highest-ranking US diplomat in Ukraine, said that Biden, one of the Democratic candidates for the 2020 presidential elections, was the main concern.

Taylor made the statements during his testimony before House of Representatives lawmakers on Wednesday, which could lead to a political trial against Trump if it is shown that he abused the power of the presidency by asking Ukraine to investigate Biden.