» Iranian Americans are detained at border with Canada.

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.

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.

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, Fouladi said.

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 Fouladi, whose group has spoken to the travelers.

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

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 CBP is detaining Iranian Americans and refusing their entry into the U.S. because of their country of origin are false,” Leas said. Officials from the agency added security at ports of entry across the country after the threat from Iran.

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. 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.