The US government placed Anwar al-Awlaki, a key leader of Al-Qaeda in the Arabian Peninsula, on its list of terrorism supporters, froze his financial assets and banned any transactions with him.

The measures were outlined in Executive Order 13224 issued Friday by the US Treasury Department.

"Anwar al-Awlaki 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.

"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."

Awlaki, now based in Yemen, rose to prominence last year after it emerged he had communicated by email with Major Nidal Hasan, a US army psychiatrist accused of opening fire on colleagues at Fort Hood, Texas, killing 13.

The imam has also been linked to Umar Farouk Abdulmutallab, a Nigerian student accused of trying to blow up a Detroit-bound flight with explosives in his underwear on December 25.