By Arshad Mohammed
WASHINGTON (Reuters) - Osama bin Laden's death sent al Qaeda into a decline that will be hard to reverse, the United States said on Tuesday in a report that found terrorist attacks last year fell to their lowest level since 2005.
Describing 2011 as a "landmark year," the United States said other top al Qaeda members killed last year included Atiyah Abd al-Rahman, reportedly the militant organization's No. 2 figure after bin Laden's death, and Anwar al-Awlaki, who led its lethal affiliate in Yemen.
"The loss of bin Laden and these other key operatives puts the network on a path of decline that will be difficult to reverse," the State Department said in its annual "Country Reports on Terrorism" document, which covers calendar year 2011.
The report attributed the killings, which included the May 2011 raid in which U.S. commandoes shot bin Laden in Pakistan, to improved cooperation on counterterrorism. But it also said al Qaeda is adaptable and poses "an enduring and serious threat."
While saying there were no terrorist attacks in the United States last year, the report said the U.S. government remains concerned about "threats to the homeland," citing the foiled 2009 Christmas Day attempt by the Nigerian "underwear bomber" who sought to blow up a Detroit-bound aircraft.
The report included a statistical annex prepared by the National Counterterrorism Center, part of the U.S. intelligence community, that showed that the overall number of terrorist attacks worldwide fell to 10,283 last year from 11,641 in 2010.
The number of worldwide fatalities fell to 12,533 last year from 13,193 the year before, according to the statistics, which NCTC issued in a report published on June 1.
That was the lowest level since 2005, when there were more than 11,000 attacks and more than 14,000 fatalities. The general decline in terrorism-related fatalities - which peaked at more than 22,000 in 2007 - reflects, in part, less violence in Iraq.
The State Department report said that as al Qaeda's "core has gotten weaker," affiliated groups have gained ground, citing al Qaeda in the Arabian Peninsula as a particular threat and voicing concern about al Qaeda in the Islamic Maghreb.
It also reported an increase in terrorist attacks in Africa, due largely to Nigeria's Boko Haram militant group, as well as in the Western Hemisphere, which it attributed chiefly to FARC insurgents in Colombia.
Daniel Benjamin, the State Department's coordinator for counterterrorism, said last year was also significant for the "Arab Spring" of popular protests and what he described as its rebuff to al Qaeda's ideology.
"We saw millions of citizens throughout the Middle East advance peaceful public demands for change without any reference to al Qaeda's incendiary world view," he said, adding upheavals also present risks.
"Revolutionary transformations have many bumps in the road," he added. "Inspiring as the moment may be, we are not blind to the attendant perils."
(Reporting by Arshad Mohammed; Editing by Cynthia Osterman and Stacey Joyce)