The United States offered bounties of $5 million each for the arrest of two Americans, including a man known as the rapping jihadist, said to have joined Islamic militants in Somalia.

Omar Hamami and Jehad Mostafa were named under the State Department's Rewards for Justice program for their ties to the Al-Qaeda linked Al-Shebab militants.

Hamami, 28, a former Alabama resident, moved to Somalia in 2006 and began to work for Shebab recruiting young trainees through his English-language rap songs and videos, the State Department said in a statement.

He was indicted in 2009 by an Alabama district court for providing support to a terrorist organization, and two years later he was placed on a US Treasury blacklist freezing all his assets in the United States.

Hamami also served as a military commander under Mostafa, a former resident of San Diego, California, who left for Somalia in 2005 where he provided media support and lead foreign fighters.

Mostafa is also on the FBI's most wanted terrorist list, and was charged in 2009 in a California district court with providing material support to Shebab.

His exact date of birth is not known, but he has said he was born in both 1981 and 1986.

Hamami -- better known as Abu Mansoor al-Amriki or "the American" -- said late last year that he had split from the insurgents, who want to kill him.

"Amriki would like to accept the honour of most wanted list and thanks everyone," he said in a message on an unverified Twitter account in November following his listing by the FBI on their Most Wanted Terrorists list.

He spends his days denouncing his former Shebab colleagues as corrupt, and refers to himself as the "former poster boy" of the group.

Since it was set up in 1984, the Rewards for Justice program has paid out over $125 million to some 80 people for information leading to the arrests of those designated as terrorists by the United States.