Published: May 18, 2011 5:35 PM EDT
Updated: May 18, 2011 5:36 PM EDT

WASHINGTON (AP) - United Airlines is apologizing for briefly restarting use of flight numbers of two planes that crashed after being hijacked on Sept. 11, 2001.

United spokesman Rahsaan Johnson says the airline regrets the recent use of flight numbers 93 and 175, and has taken steps to remove the numbers from the airline's computer system.

Johnson says the flight numbers probably went back into use just in the past few days, and he attributes it to a technical error.

The union representing United flight attendants has come out with a statement objecting to the reuse of the numbers.

United flight 93 crashed in Shanksville, Pa., and flight 175 crashed into one of the World Trade Center towers in New York.

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