The Trump administration has pushed back against the impeachment investigation of the president, accusing Democrats of bullying and intimidation in asking five diplomats to testify on White House efforts to seek dirt on potential presidential rival Joe Biden.

Secretary of State Mike Pompeo questioned the authority of three House committees conducting the impeachment probe to summon the diplomats, and said they would not appear to testify in the coming week as requested.

He also challenged the Democrat-led committees’ right to demand documents from them and suggested the administration was prepared to take the fight to court.

The committees’ request “can be understood only as an attempt to intimidate, bully and treat improperly the distinguished professionals of the Department of State” Pompeo said in a letter to Congress.

“I will not tolerate such tactics, and I will use all means at my disposal to prevent and expose any attempts to intimidate the dedicated professionals whom I am proud to lead.”

Pompeo’s comments came after Trump’s personal lawyer Rudy Giuliani suggested he might not comply with a subpoena issued by the three committees on Monday.

They want the former New York mayor to produce documents related to his efforts on Trump’s behalf to pressure Ukraine President Volodymyr Zelensky to provide dirt on Trump’s potential 2020 election rival, Democrat Joe Biden.

Giuliani alleged that the heads of the House Intelligence, Foreign Affairs and Oversight Committees had “prejudged” the case. (AFP)