A US military appeals panel has rejected an appeal by Al-Qaeda propaganda expert Ali Hamza Ahmad Suliman Bahlul, confirming his life sentence, the Pentagon announced.

In his appeal, Bahlul, a Yemeni citizen, claimed that none of the charges against him constituted war crimes that could be tried by military commission.

He also argued that the charges against him violated the US Constitution and his life sentence was "inappropriately severe and disproportionate."

But the US Court of Military Commission Review found that the "appellant’s conduct was more strategic and international in scope, and he intended to inspire and motivate an untold number of individuals to join or otherwise provide support to Al-Qaeda," according to court documents.

Pentagon spokesman Todd Breasseale said late Friday the commission also reaffirmed that Bahlul was an "unlawful enemy combatant" who provided "material support and resources" to Al-Qaeda and engaged in hostilities against the United States.

The appeals panel also ruled that Bahlul conspired with the now-dead Al-Qaeda founder, Osama bin Laden, and other members of the group, to commit murder and attack civilians "in violation of the law of war," Breasseale said.

Bahlul was initially convicted on terrorism charges and sentenced to life in prison by a US military commission operating at a detention center at the US naval base in Guantanamo Bay, Cuba, in November 2008.  He was one of the first Guantanamo detainees.