New York (AFP) - Donald Trump faced fresh protests Monday over his ban on travelers from seven Muslim countries entering the United States, a backlash that poses an enormous test for his administration.

The measures, introduced just a week after he took office, have been criticized by allies, caused confusion among border guards and galvanized Democrats looking for a way to bash Trump.

There was also growing unease among Republican lawmakers to the move.

Four federal judges moved to halt deportations, around 300 people were stopped or detained worldwide and US civil rights lawyers warned the battle could head to the Supreme Court.

A petition against Trump in Britain -- demanding that his planned state visit, announced during Prime Minister Theresa May's trip to Washington, be cancelled -- has topped one million signatures.

The European Union also vowed to ensure its citizens were not affected by any "discrimination" caused by the ban.

Thousands of noisy demonstrators poured into major airports on Sunday, showing support for immigrants and refugees affected by the US president's contentious travel restrictions.

"I just hope that we can pass this difficult period while maintaining our values as a country," said Saif Rahman, a 38-year-old Iraqi-born US citizen who was called in for additional screening after flying into Dulles airport, near Washington DC.

An executive order signed by Trump on Friday suspended the arrival of all refugees for a minimum of 120 days, Syrian refugees indefinitely and bars citizens from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen for 90 days.

While Trump cited the September 11, 2001 attacks in explaining his move, none of the hijackers' home countries -- Egypt, Lebanon, Saudi Arabia and the United Arab Emirates -- were included in the measure. All of those nations are US allies.

Lawyers accompanied by interpreters set up shop in airports and fought for the release of those detained on arrival -- many were mid-flight when Trump signed the decree.

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At least 109 people were held upon arrival to the United States despite holding valid visas. It is unclear how many are still detained.

Top Trump aides downplayed the number as "a couple of dozen" as Canada said it would offer temporary residence to those stranded in the country by the ban.

- 'Not the American way' -

Trump, a property tycoon who has never previously held elected office, sees himself making good on a key but highly controversial campaign promise to subject travelers from Muslim-majority countries to "extreme vetting".

Such steps would make America safe from "radical Islamic terrorists" he said.

He issued an official White House statement to deny it was a Muslim ban and blasted the media.

"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.

The petition in Britain, however, underscored anger at Trump's invitation to meet Queen Elizabeth II later this year.

Trump's "well-documented misogyny and vulgarity disqualifies him" from meeting the queen, it said.

And at the opening of an African Union summit in Addis Ababa feelings also ran high.

"Globally we are entering very turbulent times. The very country (where) our people were taken as slaves... has now decided to ban refugees from some of our countries," said outgoing AU Commission chair Nkosazana Dlamini-Zuma.

Trump's order -- which falls short of his campaign promise to ban all Muslims from coming to the United States -- has ignited the biggest controversy since he took office.

The president hit back on Twitter at Senators John McCain and Lindsey Graham, fellow Republicans who criticized the ban, calling them "weak on immigration".

The detention of travelers at US airports left families divided.

Six Syrians were turned away from Philadelphia International Airport and sent back to Lebanon, a Beirut airport official said.

In New York, police estimated that 10,000 people protested at Battery Park across the river from the Statue of Liberty -- America's famed beacon of freedom and immigration.

"Refugees are welcome here!" demonstrators shouted.

"It should send a chill down the spine of every American," said the city's Democratic Mayor Bill de Blasio.

Thousands more protested outside the White House.

French-American national Sarah Diligenti, who has lived in the US for 22 years, added: "I hope this is a movement that lasts. I hope it's not just a flash in the pan."

- Uncertainty reigns -

Protestors also gathered at airports in Los Angeles, Orlando and Sacramento. Hundreds demonstrated in Boston, with activists planning other rallies in Atlanta, Denver, Kansas City and Seattle.

Uncertainty remained over the ban's implementation, with some green card holders from the targeted countries saying they had been turned back or prevented from boarding flights to the US.

But the Trump administration issued a clarification late Sunday that said permanent residents would be exempt from the ban.

The order affected dual nationals, but not Canadian or US dual passport holders. Britain -- one of several countries seeking clarification from Washington -- said its nationals would not be subject to additional checks unless they traveled directly from one of the listed countries.

- Gift to extremists -

In addition to scathing criticism from abroad -- from Tehran to Cairo to major European countries -- Democratic and Republican lawmakers also hit out against the move seen by many as religious discrimination.

Sixteen attorneys general from mostly Democrat-run states vowed to fight the order as unconstitutional.

Trump appeared to justify his order by writing on Twitter that Christians in the Middle East had been "executed in large numbers."

"We cannot allow this horror to continue!" he tweeted to his nearly 23 million followers, making no mention of Muslims who have been killed in greater numbers.

Echoing comments from Iran, Yemen -- a country gripped by brutal conflict -- warned Monday that the order would "strengthen the position of extremists."

"The only way to achieve victory in the fight against terrorism... is dialogue and not creating barriers," a foreign ministry spokesman said.