Updated

WASHINGTON -- A European Union plan to partially lift a ban on passengers carrying liquids onto planes has U.S. airport officials worried that it will create a security gap and may confuse passengers traveling to the United States.

Beginning April 29, the EU plans to allow airline passengers carrying wine, perfume and other liquids purchased at duty-free shops in airports outside Europe to take those items into airline cabins with them when they catch connecting flights at about two dozen European airports.

That means, for example, that travelers flying from Asia and Africa to European airports to connect to flights to the United States can keep liquids, aerosols and gels purchased in airport duty-free shops in their carry-on bags the entire way. The items will be screened at European airports before passengers board connecting flights.

Christopher Bidwell, Airports Council International-North America's vice president for security and facilitation, said the effectiveness of the technologies European airports will use to screen liquids for explosives is unclear. There are several new technologies that European airports plan to use, he said, but none have undergone real world testing, only laboratory tests.

The Transportation Security Administration hasn't said whether passengers arriving in the U.S. from Europe with liquids purchased outside the EU will be allowed to board domestic flights with those items, but that appears unlikely, Bidwell said in an interview on Friday.

He said he's concerned passengers will become frustrated or angry if they've carried expensive items on board multiple flights for thousands of miles only to be told they have to dump them in order to board a domestic flight to reach their final destination.

"This issue points to why we have to focus on making aviation security more efficient," said Geoff Freeman, executive vice president of the U.S. Travel Association, which represents hotels, restaurants and other businesses catering to travelers. "Traveling has become too much of a hassle, and that's hampering our economic recovery."

EU airports and some European airlines have also expressed concern about the plan.

TSA spokesman Nick Kimball provided a statement that said the agency is working with the EU on security matters. He declined to answer further questions.

Victoria Day, a spokeswoman for the Air Transport Association, which represents major U.S. airlines, said it hopes Europe and the U.S. will "harmonize requirements to appropriately accommodate security and passenger-processing considerations."

The United States and the European Union restricted carry-on liquids, aerosols and gels to less than three ounces in 2006 after the British authorities uncovered a plot to bomb passenger planes bound for the United States using liquid explosives.