Dozens of Iranians and Iranian-Americans have reported being harassed or questioned for hours at the US border following heightened tensions over the US killing of Iranian General Qasem Soleimani.
The Council on American-Islamic Relations (CAIR), a Muslim advocacy group, said it had provided assistance to more than 60 travellers who were detained at length over the weekend and questioned about their political views at Washington state's border with Canada.
Many of them were reportedly denied entry to the US due to a lack of capacity for Customs and Border Patrol (CBP) to detain them.
One 24-year-old only identified as Crystal by CAIR said she was detained and interrogated for more than 10 hours with her family at the Peace Arch Border Crossing in Blaine, Washington, before being released early Sunday.
She said when the family asked why they were being detained, CBP agents said, "It is just the wrong time for you guys."
"These reports are extremely troubling and potentially constitute illegal detentions of United States citizens," said Masih Fouladi, executive director of CAIR's Washington chapter. "We are working to verify reports of a broad nationwide directive to detain Iranian-Americans at ports of entry so that we can provide community members with accurate travel guidance."
However, CBP officials have disputed the reports, saying that long delays at the border were due to increased traffic because of the holiday season and a shortage of staff to process travellers.
They also insist that the agency does not discriminate based on religion, race or ethnicity.
"Social media posts that CBP is detaining Iranian-Americans and refusing their entry into the US because of their country of origin are false," CBP spokesman Michael Friel told AFP.
He added that reports that the Department of Homeland Security and CBP had issued a directive to bar Iranian-Americans from entering the country were also false.
A security official who did not wish to be identified said that the increased delays Iranian-Americans faced at the border were related to CBP "operating with an enhanced posture at its ports of entry to safeguard our national security."
The delays at the border have been condemned by public officials, with many accusing the Trump administration of overreach.
"Washingtonians who happen to be Iranian-American were detained at the Canadian-US border for extended periods of time for no other reason than their ethnicity or country of origin," Washington Governor Jay Inslee said in a statement.
"This is wrong and rife with constitutional and moral problems," he added. "No one should be treated differently due to where they come from, how they look or what language they speak."
Senator Elizabeth Warren, a top Democratic candidate in the US presidential race, said she found the reports "deeply disturbing."
"Iranian Americans have the same rights as all other US citizens and should be treated with dignity and respect at our border -- not bigoted, xenophobic scrutiny," she said in a tweet.
The increased scrutiny at the border comes after Iran vowed to avenge Soleimani's killing in a drone strike ordered by US President Donald Trump.