Amid confusion over new United States visa rules intended to deter terrorists, a British journalist who works for the BBC was denied permission to board a flight to New York at Heathrow Airport on Tuesday because she was born in Iran.

The journalist, Rana Rahimpour, had hoped to surprise her brother in New Jersey this week by appearing at his son’s sixth birthday party with her daughter, but was turned away from her flight because of a new regulation that requires European Union citizens who are dual nationals of Iran, Iraq, Syria or Sudan, or have traveled to those countries in the past five years, to obtain a visa in advance. Other Europeans are able to travel to the United States for up to 90 days through a longstanding visa waiver program.

Ms. Rahimpour, who has not been able to travel to Iran for many years because of her work for the BBC’s Persian-language service in London, said in an email that her request for the sort of routine visa waiver that British citizens are entitled to was not denied until she appeared at the airport.