MIAMI (Reuters) - A U.S. judge declared a mistrial on Wednesday for six men accused of joining forces with al Qaeda to blow up the Sears Tower in Chicago as part of an Islamic jihad against the United States.

The Sears Tower is shown in this aerial view of Chicago July 6, 2006. REUTERS/Jason Reed

The decision was a setback for U.S. prosecutors. It was the second mistrial declared by District Court Judge Joan Lenard in the case involving the men from Miami’s impoverished Liberty City neighborhood.

U.S. authorities had billed the arrest of the men as a breakthrough in their efforts to detect and smash home-grown terrorism plots in their earliest stages, and said the defendants conspired to bomb America’s tallest skyscraper, the Sears Tower, the FBI’s Miami office and other federal buildings.

But after 13 days of deliberations, and three notes from the jury members to the judge saying they were unable to reach a verdict, Lenard declared a mistrial.

The defendants were filmed swearing an oath of allegiance to Osama bin Laden’s militant al Qaeda group, but their lawyers argued that they were only playing along in the hope of getting money out of a man claiming to have links to al Qaeda but who was actually an FBI informant.

Lenard scheduled a status conference for next Wednesday to decide whether there will be another trial for the men, who faced four terrorism-related conspiracy charges that carried a combined maximum of 70 years in prison.

The first trial in the so-called “Liberty City Seven” case ended in a mistrial in December when jurors said they were unable to reach a verdict for the same six defendants. A seventh man won acquittal at that trial.

At the time of their arrests in June 2006, federal agents said the men, who operated out of a ramshackle warehouse in Liberty City, had terrorist plans that were “aspirational rather than operational” because they had neither al Qaeda contacts nor the means of carrying out actual attacks.

Nevertheless, the arrests were presented as a major blow against terrorism.

U.S. officials denied there was any political link between the Miami case and the midterm U.S. congressional election in November 2006.

But the election came against the backdrop of a slump in President George W. Bush’s popularity and in public support for the Iraq war, and critics of the administration frequently accuse it of exploiting fear of a repeat of the September 11 attacks.

Federal prosecutors did not immediately comment on the outcome of the case on Wednesday. Lawyers for the defendants said they were unable to comment because of a gag order imposed on the case by the judge.