A U.S. counterterrorism official who asked not to be identified told the network al-Qaida seemed "content to take credit for any terrorist attacks."
The videotape aired on the Arabic al-Jazeera network Monday, showing Osama bin Laden's right-hand man, Ayman al-Zawahiri claiming the four transit system bombs were to punish Britain for its role in Iraq and Afghanistan. The July 7 attack killed 52 people.
The official said the terror group had "stepped up propaganda efforts" to get "better play" in Western media. As an example, he pointed out, al-Zawahiri's tape contained English subtitles.
Earlier this month, U.S.-born Adam Gadahn appeared on a videotape, speaking in perfect English, praising the attacks on London and Madrid and threatening future ones in Los Angeles and Melbourne, Australia.
Notable deaths of 2014 [PHOTOS]