US President Donald Trump tried to quell a huge backlash against his executive order on immigration, saying it is not a ban on Muslims.

As protesters against the order gathered at airports and poured into the streets of major US cities, Trump issued a statement last night, reiterating his position that the order is "about terror and keeping our country safe".

The US president, just 10 days in office, defended the order he signed two days earlier, saying it is similar to what former president Barack Obama did in 2011 when he banned visas for refugees from Iraq for six months.

"America is a proud nation of immigrants and we will continue to show compassion to those fleeing oppression, but we will do so while protecting our own citizens and border," Trump said in the statement.

He said the seven countries referred to in the order are the same countries previously identified by the Obama administration as sources of terror.

"To be clear, this is not a Muslim ban, as the media is falsely reporting. This is not about religion - this is about terror and keeping our country safe," he said.

Trump also said the US will again issue visas to all countries named in the order once the administration is sure it has reviewed and implemented "the most secure policies" for admitting people.

The administration earlier said the US Department of Homeland Security (DHS) would continue to enforce the ban on people arriving from Syria, Yemen, Iran, Iraq, Somalia, Libya and Sudan, despite a federal judge's order placing a hold on part of Trump's controversial order.

'Gov't retains its right to revoke visas'

"Prohibited travel will remain prohibited, and the US government retains its right to revoke visas at any time if required for national security or public safety," DHS said in a statement.

Trump's order banned citizens from the seven countries for 90 days, temporarily suspended refugee admissions for 120 days and banned admissions from Syria indefinitely.

It was challenged in court by the American Civil Liberties Union (ACLU) in New York City, and an emergency ruling on the order last Saturday night temporarily prevented refugees and immigrants from being deported.

In addition to the protests at multiple airports, there was confusion over whether people with valid visas were being detained. The confusion extended to airports outside the country where travellers were being prevented from boarding flights to the US.

Trump's executive order follows a campaign promise to temporarily ban Muslims from entering the US and review the processes used for allowing refugees in.

Only a 'couple dozen' detained

White House chief of staff Reince Priebus said yesterday that only a "couple dozen" of the 109 people who were detained as a result of the order were still being held.

"I would suspect as long as they're not awful people that they will move through" by the end of the day (yesterday), Priebus said.

Trump's order drew criticism from German Chancellor Angela Merkel and a sharp reaction from Britain, whose Foreign Secretary Boris Johnson said it was "divisive and wrong to stigmatise because of nationality."

Two senior US senators from Trump's Republican Party also criticised the order, saying they fear it will become a "self-inflicted wound in the fight against terrorism."

Senators John McCain and Lindsey Graham said the most important allies in the fight against Islamic State are Muslims who reject its apocalyptic ideology of hatred.

"This executive order sends a signal, intended or not, that America does not want Muslims coming into our country," McCain and Graham said.

Trump shot back on Twitter describing the senators as "weak on immigration," and said they "should focus their energies on ISIS, illegal immigration and border security instead of always looking to start World War III."

The top Democrat in the US Senate said he would push legislation to undo the order, and the attorneys-general of 15 US states and the District of Columbia issued a statement condemning it.

- dpa