Trump hits out again over travel ban

US President Donald Trump has defended his executive order banning most travellers from six Muslim-majority nations and criticised his own administration's revisions to the policy to address legal challenges.

In a series of tweets, Trump insisted the policy was a "travel ban," despite efforts by members of his staff to distance the White House from the politically charged term.

"The Justice Dept. should have stayed with the original Travel Ban, not the watered down, politically correct version they submitted to [the Supreme Court]," Trump said.

Trump's tweets made no mention of his own role in signing the new order and suggested he hoped to enact a tougher policy.

"The Justice Dept. should ask for an expedited hearing of the watered down Travel Ban before the Supreme Court - & seek much tougher version!" he wrote.

Trump's administration last week appealed to the Supreme Court after lower courts had temporarily frozen the implementation of his order to consider whether it violates protections on freedom of religion.

The White House downplayed discussions about whether the executive order was a travel ban, language some said would undermine its legality.

"The president doesn't care what you call it, whether you call it a ban, whether you call it a restriction," spokeswoman Sarah Sanders said. "He cares that you call it national security and that we take steps to protect the people of this country."

The Fourth Circuit Court of Appeals last month upheld a federal judge's ruling that had kept the order from going into effect.

"In any event we are EXTREME VETTING people coming into the U.S. in order to help keep our country safe. The courts are slow and political!" Trump said.

Judges in the cases have pointed to Trump's words on the campaign trail, as well as remarks by associates, calling for a ban of Muslims entering the United States to show that his intention was discrimination against Muslims rather than a legitimate exercise of his presidential powers.

The lawyer for the challengers in the Ninth Circuit pointed to Trump's tweets as evidence that the ban is discriminatory.

"Its kinda odd to have the defendant in HawaiivTrump acting as our co-counsel.We don't need the help but will take it!" attorney Neal Katyal wrote on Twitter.

Conservatives meanwhile were warning the tweets could undermine the administration's legal case.

"These tweets may make some feel better, but they certainly won't help [the solicitor general] get 5 votes in [the Supreme Court], which is what actually matters. Sad," wrote George Conway, a high-profile conservative lawyer who recently withdrew his name from consideration for a top Justice Department post and husband of Trump's advisor Kellyanne Conway.

He stressed his support for the president, but said "tweets on legal matters seriously undermine" the administration's agenda.