Traffic entering the United States from Canada at the Peace Arch Border Crossing in Blaine, Wash., in October.

More than 60 people were held for additional questioning in Washington State, according to advocacy groups and accounts from travelers.

WASHINGTON — Dozens of Iranians and Iranian-Americans were held for hours at Washington State’s border with Canada over the weekend as the Department of Homeland Security ramped up security at border ports after Iran threatened to retaliate against the United States for the strike that killed its top military leader.

More than 60 of the travelers, many returning from work trips or vacations, were trying to come home to the United States on Saturday when agents at the Peace Arch Border Crossing in Blaine, Wash., held them for additional questioning about their political views and allegiances, according to advocacy groups and accounts from travelers.

Masih Fouladi, an executive director of the Council on American-Islamic Relations, a Muslim civil rights and advocacy organization, said some were held in a waiting room and questioned for up to 10 hours. Later on Saturday night, when others who had just attended a concert in Canada by an Iranian pop star were trying to cross back into the United States, they were denied entry and told to come back later, Mr. Fouladi said.

Most of the travelers were released after the extra scrutiny, according to administration officials, although advocates said some were denied entry into the United States.

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When one family asked agents why they were being questioned, an officer told them, “This is a bad time to be an Iranian,” according to Mr. Fouladi, whose group has spoken to the travelers.

“These reports are extremely troubling and potentially constitute illegal detentions of United States citizens.”

Matt Leas, a spokesman for Customs and Border Protection, disputed the accounts and reports from advocacy groups that the Department of Homeland Security had issued a directive to detain those with Iranian heritage entering the country, despite their citizenship status.

“Social media posts that C.B.P. is detaining Iranian-Americans and refusing their entry into the U.S. because of their country of origin are false,” Mr. Leas said. Officials from the agency added security at ports of entry across the country after the threat from Iran.

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Processing time at the Blaine port of entry increased by four hours because of the high number of people entering and staffing shortages from the holiday season, according to the agency.

While border officers are not permitted to refer someone for what is known as a “secondary screening” of questioning based solely on national origin, it is one of multiple factors they are directed to consider, in addition to travel documents, travel history or suspicious behavior when choosing whom to refer for additional scrutiny. Such referrals for extra scrutiny happen daily. Gil Kerlikowske, a former commissioner of Customs and Border Protection, said agents would put an added emphasis on a traveler’s country of origin when that nation was singled out as a national security threat.

The Department of Homeland Security did just that on Saturday, when it updated its National Terrorism Advisory System to warn of Iran’s ability to retaliate against the United States through terrorism or cyberattacks or violence by homegrown extremists.

The bulletin system, which had not been updated since July, is intended to encourage law enforcement and the public to report suspicious activity.

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“If you were an Iranian citizen returning from the British Columbia, you would be sent to secondary as a result of the increased tension with that country,” Mr. Kerlikowske said. “It wouldn’t be the main factor in many cases, but certainly in this particular instance the country of origin would be the determining factor.”

Customs and Border Protection did not answer subsequent questions about whether the travelers’ country of origin played any factor in the extra scrutiny at the Blaine port.

The larger-scale detention of Iranians and Iranian-Americans seemed limited to Blaine on Sunday. Advocacy groups said they had not heard of similar incidents at airports and other ports of entry.

The travelers, some of whom asked that their full names not be published because of a fear of retaliation, said that after checking their documents, border officers would bring them inside the port to a room filled with other Iranians and Iranian-Americans.

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Sepehr Ebrahimzadeh, 33, of Seattle said he was returning from Canada on Saturday afternoon with his girlfriend after they spent a week out of town for the holidays.

With his green card and a NEXUS pass that allows expedited processing, Mr. Ebrahimzadeh has not had any troubles at the border in recent years. When a border officer referred the couple for additional scrutiny, he suspected that it was because their vehicle was messy with winter sports gear.

He thought differently once he was inside the facility and noticed people of other backgrounds getting processed quickly, while the people of Iranian descent were left waiting for hours.

When agents questioned him, they asked about the countries Mr. Ebrahimzadeh had visited in the past five years, details about his family members and whether he had a military background.

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They asked details about his father, who had performed military service before the Iranian Revolution. Mr. Ebrahimzadeh said agents did not question his girlfriend, Kathryn Teagarden, who does not have Iranian background.

Mr. Ebrahimzadeh said in an interview on Sunday that the experience had conjured up images of Japanese internment camps and left fears that the United States might prepare for war by rounding up anyone of Iranian descent.

“It’s not a pleasant thought, but it also doesn’t seem far-fetched,” he said.

The agency has in recent years rushed to aggressively question travelers at the border and airports after being surprised by major changes in national security policy, such as President Trump’s ban on travelers from seven Muslim-majority countries.

The homeland security secretary at the time, John F. Kelly, told Congress in 2017 that the agency had rushed the rollout, and the Office of the Inspector General for Homeland Security found that agents were too aggressive in preventing passengers from boarding planes bound for the United States.

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The travelers held at the Blaine port questioned whether the agency was repeating the same mistakes after Iran’s threat of a “forceful revenge” against the United States.

A woman from Kirkland, Wash., with United States citizenship said she had begun traveling home from Canada on Saturday morning after spending some time with family before her two young children were set to begin school again on Monday.

She said she got inside the border room for extra questioning a little after noon and ended up there for about six hours.

The agent who questioned her asked about her background, citizenship, military experience and details about her parents and siblings, including dates of birth and employment.

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With her 5-year-old and 7-year-old also there, the woman said she could not bring herself to explain what was happening. She said she suggested to one of them that the reason they were getting extra scrutiny was because they had chocolate in their vehicle.

But she also went outside the facility to cry so they would not see how the situation was affecting her. It was not their fault, she added, that she was born in Iran.

Darian Vaziri, 21, said he and his family arrived at the border around 8 p.m. Saturday and were also placed under further scrutiny. He said his parents were born in Tehran, and the agents asked them about where they went to school, their family members, any military background and when they were last in Iran.

Mr. Vaziri said his parents, who live in Los Angeles, had been in the United States for four decades. They had come up to Seattle to visit family and had taken a day trip to Vancouver.

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“My parents have been here for 40 years, legally, and they are still not being treated normally like everyone else,” Mr. Vaziri said.

Mr. Vaziri shared a photo of a young child who was sleeping on a bench late at night as families waited. He said one group of travelers with two young children arrived for extra scrutiny after midnight, just before he and his family were allowed to leave.

Matt Adams, the legal director for the Northwest Immigrant Rights Project, a nonprofit legal services group in Seattle involved in efforts to help people at the port of entry on Sunday, said United States citizens and permanent residents who were born in Iran or were traveling with people born in Iran were still being singled out for questioning on Sunday, but were being processed much more quickly than the night before.

Mr. Adams said that, beyond the detainment, he worried that the government might use these interrogations as tools to second-guess the immigration status of people who were lawfully in the country.

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“It’s a fishing expedition,” he said. “They are going after anyone with Iranian heritage.”

Zolan Kanno-Youngs reported from Washington, Mike Baker from Seattle and Mariel Padilla from New York. Danielle Ivory contributed reporting from New York.

Zolan Kanno-Youngs is the homeland security correspondent, based in Washington. He covers the Department of Homeland Security, immigration, border issues, transnational crime and the federal government's response to national emergencies and security threats. @KannoYoungs

Mariel Padilla is a reporter covering national breaking news for the Express desk, based in New York. @marielpadilla_

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