Donald Trump's administration will not cooperate with an impeachment inquiry being pushed by Democrats, the White House has confirmed.
Writing on behalf of the US leader, White House counsel Pat Cipollone said the probe was implemented in a way that "violates fundamental fairness".
He accused Democrats of seeking "to overturn the results of the 2016 election and deprive the American people of the president they have freely chosen".
In a letter published on Tuesday evening, Mr Cipollone wrote: "[The Democratic-led House of Representatives] have designed and implemented your inquiry in a maimer that violates fundamental fairness and constitutionally mandated due process."
Mr Cipollone also said in his view the move is also a bid to influence the 2020 presidential election.
After blasting other aspects of the investigation, he added: "President Trump and his Administration cannot participate in your partisan and unconstitutional inquiry under these circumstances."
The US leader asked Ukraine's president Volodymyr Zelenskiy to investigate his Democratic political rival Joe Biden, according to a whistleblower complaint.
Mr Trump had raised unsubstantiated allegations that the former vice-president sought to interfere with a Ukrainian prosecutor's investigation of his son, Hunter.
The conversation between the two leaders is central to the formal impeachment probe, which followed a July 25 call between Mr Trump and Ukraine's leader.
