The singer of the hit song Smile was detained for five hours upon her arrival at the Los Angeles airport.
A spokeperson for the star told People magazine, "Understandably she was upset. She has no idea why she was singled out for such treatment and found the whole experience distressing."
The star was visiting the United States, and then was on her way to Argentina where she is performing at the end of the month.
Allen reassured fans, "I want my fans to know that I will do everything I can to be back in America in September. I don’t like letting my fans down and this is a situation that I am sure we can sort."