Al Qaeda's core organization is likely incapable of carrying out another mass-casualty attack on the scale of September 11, 2001, according to the US intelligence and counterterrorism officials.

US government experts also believe that the likelihood of an attack using chemical, biological, atomic or radiological weapons over the next year was not high, said Robert Cardillo, deputy director of US National Intelligence.

Cardillo and other US officials, who spoke on condition of anonymity, described these assessments on a conference call with journalists billed as an opportunity for government experts to voice their assessments of al Qaeda's potency a year after the killing of Osama bin Laden in a US commando raid.

Cardillo said the al Qaeda "core" organization that bin Laden created has suffered strategic setbacks due to the outbreak of "Arab Spring" protests and rebellions in Islamic countries, which have not spread great sympathy for al Qaeda's hardline and violent brand of Islam.

More worrying to US counterterrorism officials and their allies abroad is the possibility of home-grown extremists, or "lone wolves," who are radicalized over the Internet or in small cells, but who also now are being given encouragement by media outlets connected to al Qaeda and its affiliates.

While they were unwilling to declare that al Qaeda was on the brink of "strategic defeat," the US officials did say they believed the central organization founded by bin Laden simply was not capable today of marshalling the kind of resources and planning that went into the deadly suicide airplane hijackings of September 11, 2001.

The officials said that the United States regards four al Qaeda spinoffs or affiliates as still posing threats of greater or lesser degree to US interests.

Most deadly, the officials said, was Yemen-based al Qaeda in the Arabian Peninsula (AQAP), which US officials believe was behind unsuccessful but imaginative attempts to attack continental US targets over the last 18 months using airplane-borne bombs stashed in a passenger's underwear and in photocopier ink cartridges.

Al Qaeda in Iraq, which arose in the wake of the 2003 US invasion to oust Saddam Hussein, remains a potentially lethal presence in that country and may be expanding its activities into neighboring Syria, though officials did not indicate they believe it poses much of a threat to US interests outside that region.

US officials said they regarded al Qaeda in the Islamic Maghreb (AQIM), an affiliate based in North Africa, as largely a criminal organization engaged in kidnapping Westerners for ransom. But they said they were concerned such tactics could evolve into more spectacular kidnappings intended to win publicity for militant causes.

US officials said that after a period in which their struggle became a magnet for disillusioned Islamic youths in both the United States and Europe, al Qaeda's Somali affiliate, al Shabaab, has seen a measurable falloff in Western recruiting and support.

On balance, a counterterrorism official said, it was "clear we've made progress towards defeating al Qaeda the organization," though elements of both the ideology and the organization certainly remain, including "a number of active networks in the United Kingdom."-Reuters