The Somalian Fifa referee who was barred from the US had his entry refused over "links to suspected members of terror organisations", the White House has said.
Omar Artan had been set to become the first Somali to officiate at the World Cup.
But he was stopped at the border while trying to enter the US - sparking a major international outcry.
Now, an American official said "derogatory information, including association with suspected members of terror organisations" was found after a search by US Customs and Border Protection (CBP).
The CBP had initially said in a statement that a Somali national arrived at Miami International Airport from Istanbul on Saturday and was deemed inadmissible due to vetting concerns.
An administration official later said CBP officials had determined that Artan was a threat to national security.
"Upon further inspection by CBP, derogatory information, including association with suspected members of terror organisations, was discovered," the official said in comments shared with reporters on condition of anonymity.
That made Artan ineligible for admission to the United States under the Immigration and Nationality Act (INA), the official added.
Omar Artan had been set to become the first Somali to officiate at the World Cup before he was stopped at the border
|GETTY
"President Trump's administration will not allow any security threat to enter our country, full stop," they vowed.
The Somali Football Federation (SFI) bemoaned the decision, labelling his initial appointment to referee at the tournament as a milestone for the East African nation.
It claimed it had not received an official explanation from Washington as to why Mr Artan was blocked from setting foot on American soil.
Somali officials are said to be continuing diplomatic efforts to allow him in in time to officiate.
WORLD CUP CONTROVERSY - READ MORE:
'President Trump's administration will not allow any security threat to enter our country, full stop,' a US official said
|GETTY
Though it was not clear which game or games Artan would have eventually refereed.
Such information is typically only announced two to three days in advance.
To ensure neutrality, match officials are barred from reffing a game involving their own national team - though Somalia failed to qualify, and has never made it to the World Cup finals.
Referees are typically restricted from officiating matches involving countries from their own confederation during the group stage, meaning Artan would not have been allowed to ref 28 of the 78 group stage fixtures.
The World Cup group stages - in full: Omar Artan would likely have been barred from refereeing 28 of the 78 group stage fixtures
|GB NEWS
A Fifa spokesman said the organisation had been told the Somali national's status "will not be changed at present".
It insisted it is "not involved in host country immigration processes, including visa adjudications".
While CBP Commissioner Rodney Scott said last night that travellers are regularly denied entry to the US because they are not eligible for entry or pose a threat.
"I don't really care what you do for a living. The law is still the law," Mr Scott told a Washington event hosted by the Centre for Immigration Studies.
"If you don't meet the qualifications to come into the country, we're not letting you in just because we want you to referee a game."