New York: A senior US congressman has urged the Australian government to be extremely careful about assisting the Trump administration's efforts to discredit the Mueller probe, warning it could "cheapen" the longstanding alliance between the two nations.

The Morrison government confirmed on Tuesday it stood "ready to assist and co-operate" with the Department of Justice investigation into the origins of the initial FBI probe into the Trump campaign's ties to Russia.

Democrat congressman Joe Courtney (front right) is co-chair of the house Friends of Australia Caucus, a key lobby group inside the Congress. Credit:AP

Joe Courtney, a six-term Democratic congressman from Connecticut, said he was deeply troubled by revelations the US President had telephoned Prime Minister Scott Morrison with the express purpose of seeking Australia's help in the investigation.

"The eyes of history are upon you and you don't want to create precedents that future prime ministers and governments feel obligated to follow," Courtney told The Sydney Morning Herald and The Age when asked how Australia should respond to the request.