Thousands of people have been mistakenly linked to names on terror watch lists when they crossed the border, boarded commercial airliners or were stopped for traffic violations, a U.S. government report says.

More than 30,000 airline passengers have asked just one agency - the Transportation Security Administration - to have their names cleared from the lists, according to the Government Accountability Office report released Friday.

Hundreds of millions of people each year are screened against the lists by Customs and Border Protection, the State Department and state and local law enforcement agencies. The lists include names of people suspected of terrorism or of possibly having links to terrorist activity.

"Misidentifications can lead to delays, intensive questioning and searches, missed flights or denied entry at the border," the report said. "Whether appropriate relief is being afforded these individuals is still an open question."

When questions arose about tens of thousands of names between December 2003 and January 2006, the names were sent back to the agencies that put them on the lists, the GAO said. Half of those were found to be misidentified, the report found.

In December 2003, disparate agencies with counterterrorism responsibilities consolidated dozens of watch lists of known or suspected terrorists into the new Terrorist Screening Center run by the FBI.

People are considered "misidentified" if they are matched to the database and then, upon further examination, are found not to match. They are usually misidentified because they have the same name as someone in the database.