A vote on calling new witnesses to testify in the impeachment trial of US President Donald Trump is likely to fail in the Senate after a Republican senator said she will not support the move, local media reported.

Senator Lisa Murkowski issued a statement on Friday saying that she will vote "against considering motions to subpoena" witnesses and documents for the Court of Impeachment.

The Democrats needed four Republicans to vote with them to allow hearing of testimony from witnesses on why Trump ordered millions of dollars in aid to Ukraine frozen.

"The House chose to send articles of impeachment that are rushed and flawed. I carefully considered the need for additional witnesses and documents, to cure the shortcomings of its process, but ultimately decided that I will vote against considering motions to subpoena," Murkowski's statement read in part.

Murkowski went on to say that she had no faith that the process will be impartial.

"I have come to the conclusion that there will be no fair trial in the Senate. I don't believe the continuation of this process will change anything."

The Democrats intended to call former US National Security Adviser John Bolton, who allegedly said that Trump had told him directly he was withholding US military aid to Ukraine until it agreed to investigate former US vice-president Joe Biden.

Source(s): ABC News