WASHINGTON (AP)  The Transportation Security Administration on Thursday dropped the subpoenas it had issued to two Internet writers in its effort to learn who leaked an airline security directive.

The agency said the investigation was “nearing a successful conclusion, and the subpoenas are no longer in effect.”

The security directive ordered extra measures after a Christmas Day attack on a Detroit-bound airliner.

One subpoena went to an Internet travel writer, Chris Elliott of Winter Springs, Fla., who did not immediately comply. Mr. Elliott said agents showed up at his house, demanding that he reveal who leaked the directive.