The singer promises fans to "do everything" she can to hit the stage here in September

By Caris Davis
Updated August 07, 2007 10:00 AM

“Smile” singer Lily Allen is trying to wear a brave face after immigration officials unexpectedly revoked her U.S. working visa as she prepares for her upcoming tour.

The perky songstress was searched and detained for five hours after being stopped at Los Angeles airport Sunday.

“Understandably she was upset,” her London rep confirms to PEOPLE. “She has no idea why she was singled out for such treatment and found the whole experience distressing.”

“I am trying everything I can to sort this situation out,” Allen said in a statement released to PEOPLE. “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.”

The entertainer, who said she had been enjoying life down under, had flown into the U.S. from Australia to attend the MTV video music awards launch in Las Vegas.

Her unscheduled meeting with U.S. officials was triggered by Immigration and Naturalization Services concerns following her arrest in London in March when she allegedly clashed with a photographer.

Allen was arrested June 28 for punching a pap in London and later posted bail. “She attended a police station on July 19 in central London and cautioned for common assault,” a police rep confirms to PEOPLE.

The 22-year-old, currently at her hotel in Los Angeles, is due to leave the U.S. and return to the U.K, within the next few days, according to her rep. She needs a new work visa to perform a string of live American dates scheduled for next month.

“It is my intention to play my American dates in September. This depends on the authorities granting me a new work visa. I want my fans to know that I will do everything I can to be back in America,” she reiterated.