NEW YORK (AP) - Mayor Michael Bloomberg says undercover investigators working for New York City were illegally allowed to buy semi-automatic pistols at an Arizona gun show.

Mayor Michael Bloomberg says that the sale not long after the mass shooting in Tucson exposes a "dangerous gap" in federal gun laws.

Bloomberg says investigators told two sellers they could probably not pass a background check for two semi-automatic pistols. He says that revelation should have prevented the sale.

 The investigators visited Phoenix on Jan. 23. That was a couple of weeks after the rampage in Tucson killed six people and wounded 13, including Rep. Gabrielle Giffords.

Bloomberg has made gun control advocacy a hallmark of his tenure. He argues that too many illegal guns end up on city streets.

(Copyright 2011 by The Associated Press. All Rights Reserved.)