A Californian relative of a British family which was refused entry to the United States for a holiday has told the BBC the US government must explain its actions.
Muhammad Tahir Mahmood said his children had been looking forward to welcoming their cousins and were sad that the trip had been cancelled.
Mr Mahmood, 47, said he had been preparing to welcome his two brothers, Zahid and Tariq, their seven children and two of his sister's children for the holidays.
They had planned to go sky-diving and to make trips to several California theme parks, he said.
Mr Mahmood, a US citizen who runs a car repair business in San Bernardino, said he could think of no reason why his relatives would represent a threat to the country and called on his government to explain its actions.
"They can get away with anything by saying national security… and you cannot even challenge that," he told BBC News, adding: "There is no check and balance."
A spokesperson for US Customs and Border Protection refused to comment on this specific case, but told the BBC people travelling to the US "bear the burden of proof to establish that they are clearly eligible to enter the United States... the applicant must overcome all grounds of inadmissibility."
Categories of inadmissibility include, among others: health-related reasons, criminal convictions, public charge, security reasons and labour certification.
In the UK, Labour MP Stella Creasy called on the prime minister to challenge the US, calling it "a growing problem" of British Muslims being barred from the US without explanation.
She also told BBC Radio 5 live she was aware of four other UK cases of Muslims who were denied entry to the US.
"Nobody knows why these people were stopped. We do know what the common denominator is between them. All of us agree we've absolutely got to be vigilant about tackling terrorism, and we've got to be clear prejudice hasn't got a part to play in that," she said.
Mr Mahmood said he prayed at the same mosque as Syed Rizwan Farook, who along with his wife Tashfeen Malik killed 14 people in San Bernardino on 2 December but he "did not know him personally", would not have recognised him and could not recall ever speaking to him.
The couple died in a shootout with police a few hours after the attack, which is being investigated by the FBI as an act of Islamist terrorism.
Mr Mahmood said he had no problem with the US denying entry to people who were deemed to be threats but he insisted: "There needs to be a reason given."
Americans expected their country to act according to due process, said Mr Mahmood, who moved to the US from Pakistan more than 20 years ago.
"I think that's what the democracy stands for, run by the people, for the people," he said. "The authorities need to tell people why they're not letting people in."
Mr Mahmood said he could only surmise that his relatives had been refused entry because of an atmosphere of "Islamophobia" on the day the California public school system was disrupted by a threat, an atmosphere which he said had been fostered by hostile and unfair reporting about Muslims.
Muslims in America - in-depth
"It's a scary thing being a Muslim in America," the father of three told the BBC, adding that the media was "painting Islam as the enemy" when in fact Muslims were peace-loving people who had nothing to do with the actions of individual "idiots".
He said he was extremely worried about where the country was heading and there was a perception that "it's very dangerous to be a Muslim in America" because of media reporting and inflammatory rhetoric from politicians including Donald Trump.
"Every country, every race, every religion has idiots and Trump is one of the American idiots," he said.
Most American people were "very educated, very good people" and they realise that, he added.
Mr Mahmood said the last time he returned to the US from the UK he had been pulled aside at an airport for lengthy questioning because he was a "Muslim, bearded, brown" guy. "I expected that," he said, "but it's difficult to explain to the children."