US President Donald Trump has ramped up his criticism of a federal judge who blocked a travel ban on seven mainly Muslim nations, intensifying the first major legal battle of his presidency.

In a series of tweets that broadened his attack on the country's judiciary, Trump said Americans should blame US District Judge James Robart and the court system if anything happened.

Trump did not elaborate on what threats the country potentially faced. He added that he had told the Department of Homeland Security to "check people coming into our country VERY CAREFULLY. The courts are making the job very difficult!"

The Republican president labelled Robart a "so-called judge" yesterday, a day after the Seattle-based jurist issued a temporary restraining order on a 90-day ban affecting citizens from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen and a 120-day bar on all refugees.

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A US appeals court last night denied the Government's request for an immediate stay of the ruling.

Vice-President Mike Pence defended Trump today, even as some Republicans encouraged the President to tone down his broadsides against the judicial branch of government.

"The president of the United States has every right to criticise the other two branches of government," Pence said on NBC's Meet the Press.

It is unusual for a sitting president to attack a member of the judiciary, which the US Constitution designates as a check on the power of the executive branch and Congress.

US Senator Patrick Leahy, the ranking Democrat on the Senate Judiciary Committee, said Trump seems intent on precipitating a constitutional crisis.







Some Republicans also expressed discomfort with the situation.

"I think it is best not to single out judges for criticism," Senate Majority Leader Mitch McConnell said on CNN's State of the Union.

"We all get disappointed from time to time at the outcome in courts on things that we care about. But I think it is best to avoid criticising judges individually."

The ruling by Robart, appointed by former Republican President George W. Bush, along with the decision by the 9th US Circuit Court of Appeals in San Francisco to deny the Government's request for an immediate stay dealt a blow to Trump barely two weeks into his presidency.

It could also be the precursor to months of legal challenges to Trump's push to clamp down on immigration, including through the construction of a wall on the US-Mexican border.

- AAP