The officials asked not to be not be identified because of the sensitive nature of the information. They both stressed the effort is aimed at being ready with options for the White House if President Obama orders a retaliatory strike. The effort is to see whether targets can be specifically linked to the airliner incident and its planning.

U.S. special operations forces and intelligence agencies, and their Yemeni counterparts, are working to identify potential al Qaeda targets in Yemen, one of the officials said. This is part of a new classified agreement with the Yemeni government that the two countries will work together and that the U.S. will remain publicly silent on its role in providing intelligence and weapons to conduct strikes.