Al-Awlaki is thought to be hiding in Yemen and he has been placed on a secret U.S. government list of targets to be captured or killed, according to U.S. officials. He is also believed to have exchanged e-mails with an Army psychiatrist charged with killing 13 people in last November's Fort Hood shootings and he is accused of helping inspire the Times Square bombing attempt in May

Born in New Mexico, al-Awlaki, 39, is not perceived by American officials as a major tactical terror leader on a par with al Qaeda founder Osama bin Laden. But his role as an inspirational exhorter for al Qaeda's cause and his growing involvement in plots aimed at the U.S. has made him a prime target in the effort to counter the militant movement.

Treasury officials Friday cited the cleric for his operational role in aidingal Qaeda's growing faction in Yemen. Al-Awlaki has pledged an oath of loyalty to the faction, al Qaeda in the Arab Peninsula, and he has "facilitated training at camps in Yemen in support of acts of terroroism and helped focus AQAP's attention on planning attacks on U.S.interests," the agency said.

"Anwar al-Awlaki has proven that he is extremely dangerous, committed to carrying out deadly attacks on Americans and others worldwide," saidStuart Levey, Treasury's undersecretary for Terrorism and Financial Intelligence. "He has involved himself in every aspect of the supply chain of terrorism — fundraising for terrorist groups, recruiting and training operatives and planning and ordering attacks on innocents."

Members of al-Awlaki's tribe in Yemen have denied he is connected to al Qaeda despite a video posting he issued last month calling for the killing of Americans. In the recent 45-minute video, al-Awlaki said U.S. deaths are justified and encouraged, citing what he said was U.S. intentional killing of a million Muslim civilians in Iraq, Afghanistan and elsewhere.

Treasury officials Friday cited al-Awlaki's purported involvement in theChristmas Day plot to bring down a Detroit-bound U.S. airliner, saying that he prepared bombing suspect Umar Faruk Abdulmuttallab for the operation to detonate explosives hidden in his underwear.

After receiving directions from al-Awlaki, officials said, Abdulmuttalab obtained the explosive device he hid in his underwear before trying to detonate it on board the flight. The explosive did not ignite and the suspect was arrested after landing.

Treasury also cites al-Awlaki's 2006 imprisonment in Yemen on charges of kidnapping for ransom and his role in a plot to kidnap a U.S. official. The cleric was released in December 2007 and then went into hiding.

"Al-Awlaki has sought to encourage his supporters to provide money for terrorist causes," Levey said. "Those who provide material support to al-Awlaki or AQAP violate sanctions and expose themselves to serious consequences."