The White House has said a five-year-old boy was detained for more than four hours and reportedly handcuffed at an airport because he posed a “security risk”.

The boy, reportedly a US citizen with an Iranian mother, was one of more than 100 people detained following President Donald Trump’s immigration order.

In a press briefing, Mr Trump’s press secretary Sean Spicer was unrepentant about the incident.

He said: “To assume that just because of someone’s age and gender that they don’t pose a threat would be misguided and wrong.”

Footage shows the boy's mother waiting anxiously at Dulles International airport in Washington DC before being reunited with her son, who was reportedly flown into the airport with another family.

She then sang “happy birthday” to the little boy in English as she hugged him and covered him with kisses as onlookers cheered.

Iranian mother reunited with 5-year-old son after he was detained at Dulles Airport

The mother declined to speak with reporters, but Senator Chris Van Hollen said the little boy was a US citizen who lives with his mother in Maryland.

Mr Van Hollen, a Democrat, said it was “outrageous” that the boy had been held for so long and that his mother had given the airport advance notice of his arrival.

Anger has continued to grow over Mr Trump’s executive order which has temporarily barred citizens of seven Muslim majority countries and all refugees from entering the country.

The order also indefinitely prohibits Syrian refugees from entering the US.

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Several lawsuits have been filed in the US and refugee groups around the world have condemned the move as unethical, unjustified and as being in breach of international and US law.

Mr Trump has stridently defended the policy, which he indicated he would introduce throughout his election campaign.