Washington: The White House declared on Tuesday it will not co-operate with what it termed an "illegitimate" impeachment probe by House Democrats, setting up a constitutional clash between President Donald Trump and Congress.

Trump attorneys sent a letter to House leaders bluntly stating their refusal to participate in the quickly moving impeachment investigation.

The letter threatens to cease co-operation with Capitol Hill on key oversight matters, accusing lawmakers of formulating their probe "in a manner that violates fundamental fairness and constitutionally mandated due process".

"Given that your inquiry lacks any legitimate constitutional foundation, any pretense of fairness, or even the most elementary due process protections, the Executive Branch cannot be expected to participate in it," White House counsel Pat Cipollone wrote.