President Donald Trump has defended his controversial immigration ban, denying it is to blame for the chaos at US airports over the weekend and instead blaming computer glitches, protesters and the "tears" of a senator.

Key points: Donald Trump said only 109 out of 325,000 people "were detained and held for questioning"

Donald Trump said only 109 out of 325,000 people "were detained and held for questioning" The White House maintains the ban is to keep America safe

The White House maintains the ban is to keep America safe The order has sparked protests and criticism from around the world

Mr Trump signed an executive order which temporarily banned the entry of refugees and people from seven Muslim-majority countries, sparking protests and drawing criticism from governments in London and Berlin to Jakarta and Tehran.

Protesters have flooded the streets in major cities across the United Kingdom and Canada calling for Mr Trump to be impeached and the restrictions to be repealed.

The order was partially blocked by a federal judge's ruling that stranded travellers could stay in the country, and Mr Trump later tempered a key element of the ban which prohibited those with green cards from re-entering the US.

But the President took to Twitter with a flurry of tweets defending the order.

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"There is nothing nice about searching for terrorists before they can enter the country," he tweeted.

"This was a big part of my campaign. Study the world!"

He also defended the timing of the order, saying it was to stop "the bad" from rushing into the country.

Sorry, this video has expired Travel ban 'blown way out of proportion'

He said only 109 out of 325,000 travellers "were detained and held for questioning" following his ruling.

"Big problems at airports were caused by Delta computer outage, protesters and the tears of Senator Schumer," he added, referring to a systems outage on Sunday night that led to departure delays and cancellations of at least 150 Delta Air Lines flights.

However, the chaos started on Saturday as protesters packed some of the country's major airports to demonstrate against the executive order.

Democratic senator Chuck Schumer earlier teared up on camera as he seethed over the "mean-spirited and un-American" immigration ban.

He was among several Democrats in Congress who said they would be introducing legislation to stop the ban.

Some Republicans in Congress urged caution amid legal challenges to the order, although top congressional Republicans largely remained behind Mr Trump on the issue.

Protesters have flooded the streets in major cities across the United Kingdom. ( Reuters: Dylan Martinez )

McCain, Obama denounce Trump's policy

The order drew criticism from senior Republican senator John McCain, who warned it could serve as propaganda for terrorists, and Canada, which offered temporary residency to stranded travellers.

Mr Trump has compared his policy to that of former president Barack Obama's in 2011, a claim which Mr Obama has rejected.

Mr Obama is heartened by the political activism he sees across the country and "fundamentally disagrees with the notion of discriminating against individuals because of their faith or religion", spokesman Kevin Lewis said.

"Citizens exercising their Constitutional right to assemble, organise and have their voices heard by their elected officials is exactly what we expect to see when American values are at stake," Mr Lewis said.

European Union officials denounced the policy as a dangerous embrace of isolationism and inequality, while the international aid group Doctors Without Borders accused Mr Trump of keeping people "trapped in war zones, directly endangering their lives".

In Iraq, two politicians said the Iraqi parliament had approved a "reciprocity measure" restricting the entry of Americans into Iraq.

The Trump administration declared the order's implementation "a massive success story", claiming it had been done "seamlessly and with extraordinary professionalism".

Washington state's Attorney-General announced he was suing Mr Trump over the executive order.

Attorney-General Bob Ferguson became the first state attorney-general to announce a legal action against the Trump administration over one of its policies.

The developments came after a federal judge in New York issued an emergency order temporarily barring the US from deporting people from the seven majority Muslim nations subject to Mr Trump's 90-day travel ban.

The order barred US border agents from removing anyone who arrived in the US with a valid visa from Iraq, Syria, Iran, Sudan, Libya, Somalia and Yemen.

It also covered anyone with an approved refugee application.

The Department of Homeland Security said the court ruling would not affect the overall implementation of the White House order.

Sorry, this video has expired San Francisco protests against Trump's refugee ban

AP/Reuters