Usama bin Laden and other Al Qaeda leaders are believed to be providing strategic and philosophical guidance from Pakistan to Yemen-based Al Qaeda in the Arabian Peninsula, or AQAP, the group Washington believes was behind last week's attempt to ship bombs in packages to the U.S.
Increased communication and collaboration between Al Qaeda militants in Yemen and the group's central leadership have fueled alarm about terrorist plots which U.S. and European officials first detected months ago and which they believe remain active despite efforts to thwart them.
Some officials said the release of a bin Laden audiotape last week might have been the signal for AQAP to set the package-bomb plot in motion, though others said it was too soon to tell whether there was a direct connection.
Seen as Al Qaeda's most active and ambitious affiliate, AQAP has at times sought the blessing of Mr. bin Laden on leadership decisions. Direct command-and-control for terror operations is believed to rest chiefly with the local affiliate, officials said.
Officials say their knowledge about suspected ongoing plots in Europe is limited. Security concerns have been heightened further by a spate of mail-bomb attempts this week that appeared to target European leaders and institutions, and the disclosure that Britain arrested a member of AQAP earlier this year for allegedly plotting a U.K. attack.
U.S. officials have kept in place a broad travel alert issued on Oct. 3 advising Americans to show vigilance when traveling in Europe. One of the plots of concern, officials say, is a potential Al Qaeda attack in the U.K., Germany or France modeled after the siege on Mumbai in 2008 that killed over 160 people.
"Nobody thinks last week was the whole enchilada," a senior counterterrorism official said of the cargo-bombing plot. "There are still things in play."
Officials said counterterrorism operations in Pakistan don't appear to have disrupted the multiple plots, in part because sleeper cells may already be in place in European cities. European authorities have launched an expanded manhunt for individuals who may be involved.