Organisers and activists have warned that immigration authorities in the United States detained and questioned at length dozens of individuals owing to their Iranian descent, a claim that Customs and Border Patrol dismissed as "false".

Activists and the Washington chapter of the Council on American-Islamic Relations (CAIR-WA) said immigration authorities detained and questioned at least 60 Iranians and Iranian-Americans over the weekend at the Peace Arch Border Crossing in Blaine, Washington. The watchdog group said some were held and questioned for at least 11 hours.

More:

A US Customs and Border Protection (CBP) spokesperson dismissed as "false" social media posts purporting that Iranian Americans were detained and refused entry because of their ethnic origins.

The spokesperson added that "reports that DHS/CBP has issued a related directive are also false". The spokesperson was referring to allegations made by CAIR, who cited an unnamed source at CBP, that the Department of Homeland Security (DHS) issued a national order for CBP to report and detain individuals of Iranian origin entering the country who are deemed "adversarial".

CAIR said one woman, identified as a 24-year-old American medical student named Crystal, was detained for 10 hours with her family before being released.

Crystal's family reached out to the Iranian-American writer and community organiser Hoda Katebi, who then took the matter to CAIR-WA.

Katebi said by the time she was contacted by Crystal's family, they were at the facility for five hours. "Other people were already there for eight to nine hours," she said.

According to CBP, wait times at the Blaine facility were on average two hours on Saturday evening, but some travellers had to wait up to four hours due to an increased number of people trying to go through the port of entry and reduced staffing during the holiday season.

Citing individuals she spoke with and assisted, Katebi said the questions asked of those of Iranian origin had nothing to do with immigration.

"They were asked [about] specific organisations, and political factions in Iran and their affiliations with them or their views on them or groups that they never even heard of," Katebi said the individuals she assisted said. She also said they were asked about their college majors. Katebi said she feared such questions were geared to "finding reasons to find an Iranian suspicious".

Robert McCaw, CAIR government affairs director, said: "This is the type of scenario that CAIR monitors for after US foreign entanglement with Muslim countries".

Tensions with Iran and the United States escalated dramatically last week after President Donald Trump ordered the killing of Qassem Soleimani, a top Iranian military commander, in Iraq. Iran has promised severe retaliation.

CBP said: "Based on the current threat environment, CBP is operating with an enhanced posture at its ports of entry to safeguard our national security and protect the America people while simultaneously protecting the civil rights and liberties of everyone."

On Saturday, DHS said at this time "there is no specific, credible threat against the homeland".

Several US politicians commented on the reports of detentions at the Washington-Canada border, including Washington US Congresswoman Pramila Jayapal, who said she was "deeply disturbed".

Washington Governor Jay Inslee said on Twitter that his office is "closely tracking reports that Iranian Americans, including US citizens and lawful permanent residents, have been detained.'' He urged anyone affected to contact his office.

Editor's note: A previous version of this article listed Washington state as Washington, DC. This mistake was made during the editing process and has been corrected throughout.