|Robert Mueller, the FBI director, testified before a US senate hearing on homeland security [Reuters]
US authorities are having a harder time detecting terrorism threats on American soil, even though they believe that al-Qaeda in Pakistan is at one of its weakest points.
Speaking at a US Senate hearing on Wednesday, Michael Leiter, the chief of the US counter-terrorism centre, said that the al-Qaeda threat to the United States had grown more complex in the past year and emphasised the challenges of pinpointing and blocking terrorist plots.
Nonetheless, Leiter said, the terrorist group remains capable and determined enemy that has proven its resilience over time.
"Groups affiliated with al-Qaeda are now actively targeting the United States and looking to use Americans or Westerners who are able to remain undetected by heightened security measures," said Robert Mueller, the FBI director.
Mueller told lawmakers that the main concern now was from al-Qaeda affiliates in Pakistan, Afghanistan, Yemen, Somalia and Iraq.
Hard to detect
Janet Napolitano, the Homeland Security secretary, said al-Qaeda had inspired an array of terrorist groups.
"The threat is evolving in several ways that make it more difficult for law enforcement or the intelligence community to detect and disrupt plots," Napolitano said in a written testimony submitted to the Senate Committee on Homeland Security and Government Affairs.
"The threats come from a broader array of groups and regions. It comes from a wider variety of harder-to-detect tactics. And it is aimed at harder-to-secure places than before," she added.
But Napolitano said the failed May 1 car bombing in New York's Times Square and the December 25, 2009, attempt to bomb a Detroit-bound airliner showed a shift toward attacks that require less extensive planning and coordination.
Both attacks caught US authorities off guard. As a result, Napolitano warned that the US faces a growing threat from roadside bombs like those used in Iraq and Afghanistan, as well as small arms attacks of the kind used in devastating attacks such as the 2008 Mumbai attacks that killed 166 people in India.
The list of potential targets now includes hotels, sports stadiums and other public areas as well as famous landmarks, airliners, chemical plants and ports.
"Unlike large-scale, coordinated, catastrophic attacks, executing smaller-scale attacks requires less planning and fewer pre-operational steps. Accordingly, there are fewer opportunities to detect such an attack before it occurs," Napolitano said.
The threat of homegrown terrorism has also taken on a higher profile with the March indictment of Colleen LaRose, a blond Pennsylvania woman known as "Jihad Jane," who is accused of plotting over the Internet to kill a Swedish cartoonist for depicting the Prophet Mohammed in a manner offensive to Muslims.
Plots by US citizens or residents over the past year "surpassed the number and pace of attempted attacks during any year since 9/11," Leiter said.
About two dozen Americans have been arrested on terrorism charges since 2009, according to Napolitano.
"While it is not clear if this represents an actual increase in violent radicalisation ... it is nonetheless evident that over the past 12 months efforts by violent extremist groups and movements to communicate with and recruit individuals within the United States have intensified."
She added the threat was "directed at the West generally". Napolitano is expected to discuss the issue with her European counterparts next week.