SEATTLE -- Civil rights groups and lawmakers demanded information from federal officials Monday following reports that dozens of Iranian-Americans were held up and questioned at the border as they returned to the United States from Canada over the weekend.

The Washington state chapter of the Council on American-Islamic Relations said more than 60 Iranians and Iranian-Americans were detained and questioned for hours at the Peace Arch Border Crossing in Blaine, Wash. The delays followed security warnings that Iran might retaliate for President Donald Trump's decision to kill a top Iranian general last week.

Some of the travellers were returning from a concert by an Iranian pop star in Vancouver, B.C., on Saturday night, while others had been vacationing or visiting relatives over the holidays.

Unusual delays in clearing travellers of Iranian descent continued until Sunday afternoon but appeared to have ended by Monday, the civil rights groups said. It was not immediately clear if travellers had been similarly delayed elsewhere.

Border agents typically have discretion to refer a traveller for additional inspection, such as when a traveller's paperwork is not in order or if something raises the agent's suspicion. But immigrant rights groups and lawmakers said singling out Iranian-Americans absent such factors was wrong and violated their right to equal protection under the law.

Negah Hekmati, 38, told a news conference at the Seattle office of U.S. Rep. Pramila Jayapal on Monday that she and her husband were detained, along with their 8-year-old son and 5-year-old daughter, from midnight to 5 a.m. Sunday as they returned from a ski trip. They are all U.S. citizens, though she and her husband were born in Iran.

The family is in the NEXUS program - an expedited border-crossing program for low-risk travellers - and visits relatives in Canada about once a month, she said. They had never previously been detained for so long.

"My daughter was telling me, 'Please don't speak Farsi. Maybe if you don't speak Farsi they won't take you,"' said Hekmati. "This is not OK."

Border guards took their passports, NEXUS cards and car keys, she said. They questioned her about her parents, her education and her Facebook and email accounts, she said, and asked her husband about the military service he was required to perform in Iran as a young man.

Another family they were travelling with was similarly detained, and they said they saw about two dozen other families - all of Iranian descent - in the same waiting area, Hekmati said. Only one white family passed through the area while they were there, she said, and that family was allowed to leave within minutes.

Michael Friel, a spokesman for U.S. Customs and Border Protection, said reports that Iranian-Americans were detained or refused entry because of where they were born were not true.

"'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," Friel said in a statement.

He said border wait times increased to an average of two hours Saturday evening at Blaine, Washington, because of increased traffic and reduced staffing because of the holiday season.

Jayapal and others rejected the assertion that low staffing levels had anything to do with the singling out of Iranian or Iranian-American families. She suggested the Department of Homeland Security, which includes Customs and Border Protection, was lying.

"DHS was the same agency that denied family separations were happening" on the southern border, she noted.

Washington Gov. Jay Inslee, a Democrat, tweeted Sunday that his office was trying to speak with people who experienced problems and was asking federal government officials for more information.

Jorge Baron, executive director of the Northwest Immigrant Rights Project, said he went to the border crossing at Blaine on Sunday in response to the reports. He tweeted that he spoke with one legal permanent resident of the U.S. who was detained for 11 hours overnight in "secondary screening" along with about 40 other people who had been born in Iran.

"Bottom-line: despite CBP denials, this was definitely happening," Baron wrote.

He reported meeting with three families - all U.S. citizens or legal permanent residents - who had been delayed as long as 2 1/2 hours.

"CBP claims that they were not 'detaining' people but this is only true if you define 'detain' to mean only to be placed in a locked room," Baron tweeted. "These individuals were in a waiting area and could walk to the parking lot but were not free to go: They were not being allowed to enter the U.S. (their only home) and CBP was holding their passports so they couldn't back to Canada even if they had wanted to."