The Treasury Department on Friday formally designated Yemen-based Anwar al-Aulaqi as a supporter of terrorism and froze any assets he has under U.S. jurisdiction.

The American-born 39-year-old is a “key leader” of Yemen-based al-Qa'ida in the Arabian Peninsula, which has claimed responsibility for attacks in several nations, Treasury said.

Al-Aulaqi – or al-Awlaki – has played an “increasingly operational role” in the group and helped prepare Umar Farouk Abdulmutallab for his failed attempt to blow up a Detroit-bound plane on Christmas Day last year, Treasury alleged.

The government action Friday also bars Americans from any transactions with Al-Aulaqi.

"Anwar al-Aulaqi has proven that he is extraordinarily dangerous, committed to carrying out deadly attacks on Americans and others worldwide," said Under Secretary for Terrorism and Financial Intelligence Stuart Levey in a statement.

"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,” he added.

Treasury said al-Aulaqi plays a major role in setting the “strategic direction” for the Yemen-based terror group, and has also recruited members and “facilitated” training camps.

White House Press Secretary Robert Gibbs said in May that the U.S. is “actively” hunting for al-Aulaqi, and the U.S. has authorized operations to kill or capture him, according to numerous press reports.