By Jane Sutton

MIAMI (Reuters) - A U.S. appeals court on Friday overturned the Guantanamo war crimes conviction of an al Qaeda videographer, a ruling likely to lead to dismissal of conspiracy charges in the pending trial of five men accused of plotting the September 11 attacks.

The Court of Appeals for the District of Columbia threw out the conviction of Yemeni prisoner Ali Hamza al Bahlul, ruling that the charges of which he was convicted - conspiracy, providing material support for terrorism and soliciting murder - were not internationally recognized as war crimes when the acts were committed.

Bahlul is serving a life sentence in the detention center at the Guantanamo Bay U.S. Naval Base in Cuba.

He acted as a publicist for Osama bin Laden's al Qaeda organization, making recruiting videos and taping the wills of some of the hijackers who slammed commercial jetliners into the World Trade Center, the Pentagon and a Pennsylvania field on September 11, 2001.

The same appeals court threw out the Guantanamo conviction of one of bin Laden's drivers, Salim Hamdan, in October, on similar grounds.

Prosecutors had expected the decision and have asked that conspiracy charges be dropped against the alleged mastermind of the September 11 plot, Khalid Sheikh Mohammed, and four other men facing trial at Guantanamo.

Defense attorneys said the judge in that case was expected to grant the request at a pretrial hearing next week. The defendants in that case could still face the death penalty if convicted on other charges that include 2,976 counts of murder.

The widely criticized Guantanamo court was established after the 2001 attacks to try foreign captives on terrorism-related charges outside the regular U.S. civilian and military courts. It has completed only seven cases, and defense attorneys said the appeals court rulings had essentially nullified five of them.

(Editing by Peter Cooney)