Yemen had already intensified operations against al-Qaeda in late 2009 , when a Yemen-based wing of the group claimed to be behind the failed 25 December 2009 attempt to blow up a Detroit-bound U.S. airliner , itself a retaliation against an attack against a training camp in Abyan on 17 December , killing many civilians . News reports have indicated substantial American involvement in support of Yemeni operations against al Qaeda since late 2009 , including training , intelligence sharing , " several dozen troops " from the Joint Special Operations Command , and limited direct involvement in counterterrorism operations
attempt to blow up
Northwest Airlines Flight 253
Al-Qaeda insurgency in Yemen