About 900 US State Department officials signed an internal dissent memo protesting a travel ban by US President Donald Trump on refugees and travellers from seven Muslim-majority countries, a source familiar with the document said yesterday, in a rebellion against the new president's policies.

A senior State Department official confirmed the memorandum had been submitted to acting Secretary of State Tom Shannon through the department's "dissent channel," a process in which officials can express unhappiness over policy.

White House spokesperson Sean Spicer said on Monday he was aware of the memo but warned career diplomats that they should either "get with the programme or they can go".

A draft of the dissent memo seen by Reuters argued that the executive order would sour relations with affected countries, inflame anti-American sentiment and hurt those who sought to visit the United States for humanitarian reasons.

It said the policy "runs counter to core American values of non-discrimination, fair play and extending a warm welcome to foreign visitors and immigrants".

Trump on Friday signed an executive order that temporarily bans refugees and people from seven Muslim-majority countries, sparking tumult at US airports and protests in major American cities.

The ban affects Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen.

Even before the executive order on immigration was issued, concern among State Department officials had been growing over news reports that Trump was about to ease sanctions against Russia, said one State Department official said, speaking on condition of anonymity.

The resignation of at least four top State Department officials, including Under-Secretary for Management Patrick Kennedy, who formally left the department yesterday, also caused some unease among diplomats who worried about a power vacuum.

- Reuters