NEW YORK: A son-in-law of Osama bin Laden who acted as a spokesman for al Qaeda, pleaded not guilty in federal court on Friday to conspiracy to kill Americans.

Suleiman Abu Ghaith, a militant who appeared in videos representing al Qaeda after the Sept. 11, 2001 attacks, made his initial appearance in a Manhattan courthouse only blocks from the site of the World Trade Center.

US prosecutors said they expected the trial to last three weeks, but no starting date was scheduled. They said the date would be set in April.

Abu Ghaith, who was arrested in Turkey, is one of the highest-ranking al Qaeda figures to be brought to the United States to face a civilian trial. Evidence against him includes videos and audio recordings, prosecutors said.

“Among other things, Abu Ghaith urged others to swear allegiance to bin Laden, spoke on behalf of and in support of al Qaeda's mission, and warned that attacks similar to those of September 11, 2001 would continue,” according to the indictment, which was announced on Thursday.

It accuses him of acting in a conspiracy that “would and did murder United States nationals anywhere in the world,” listing actions before and after Sept. 11, 2001.

US Attorney General Eric Holder previously had announced plans to try defendants in the Sept. 11 attacks in the same federal courthouse where Abu Ghaith appeared.

But public opposition forced him to back down, and the trials were moved to the US military base at Guantanamo Bay, Cuba.