Washington has added a US-born Muslim cleric linked to al-Qaeda to its terrorism blacklist and imposed financial sanctions on him.

The move would freeze any US assets of Anwar al-Awlaki, prevent him from travelling to the US and bar Americans from sending him money.

Mr al-Awlaki is suspected of helping plan the failed bombing of an airliner over Detroit last Christmas.

He is thought to be in Yemen with al-Qaeda in the Arabian Peninsula.

US officials have warned Yemen is becoming a safe haven for al-Qaeda militants.