A former spokesman for al-Qaeda and son-in-law of Osama bin Laden pleaded not guilty Friday to a charge that he conspired to kill Americans.

The plea in federal court in Manhattan was accompanied by new indications that the former spokesman, Sulaiman Abu Ghaith, has cooperated with U.S. authorities while being secretly held in U.S. custody since his Feb. 28 arrest in Jordan.

Assistant U.S. Attorney John P. Cronan said Abu Ghaith had given an “extensive post-arrest statement” that spans 22 pages. Cronan offered no details on what the former member of al-Qaeda’s inner circle revealed, but indicated that Abu Ghaith has been in the United States — presumably in the Metropolitan Correctional Center in Manhattan — since March 1.

The decision to bring Abu Ghaith directly to the United States suggests that he was not seen as a source of intelligence on current al-Qaeda operations. Under an interrogation program authorized by President Obama in 2009, authorities could have chosen to hold Abu Ghaith for an extended period overseas.

Officials at the CIA and FBI declined to comment.

Abu Ghaith, 47, has spent much of the past decade under a form of house arrest in Iran alongside other former senior members of al-Qaeda who fled Afghanistan after the U.S.-led invasion in 2001.

The group, described by U.S. intelligence officials as an al-Qaeda “management council,” was kept under tight supervision by Iranian authorities and largely cut off from the rest of the terrorist network, U.S. officials said.

A separate, lower-level al-Qaeda group in Iran has had greater latitude, U.S. officials said, helping to route volunteers and resources to al-Qaeda’s base in Pakistan.

Abu Ghaith appears to know little about the operations of that cell, officials said, and the single charge he faces stems from his alleged role assisting bin Laden and urging others to swear allegiance to al-Qaeda in 2001.

In his court appearance, Abu Ghaith relied on a translator to relay questions from Judge Lewis A. Kaplan, nodding yes that he understood his rights and no when asked whether he had money to hire an attorney, according to an account by the Associated Press. He entered a plea of not guilty through his court-appointed lawyer, Philip Weinstein.

Another pretrial hearing has been scheduled for April 8.

A former Muslim cleric and native of Kuwait, Abu Ghaith is believed to have joined al-Qaeda in Afghanistan in 2000. He married bin Laden’s eldest daughter, Fatima, and was a prominent spokesman for the group after the Sept. 11, 2001, attacks.

In one message he warned Americans that “the storms shall not stop, especially the airplanes storm.”

It is unclear when or how he left Iran before being detained in Turkey last month. He was taken into U.S. custody in Jordan while being deported to Kuwait, U.S. officials said.

A report that was posted on a jihadist Web site and that surfaced Friday claimed that Abu Ghaith had been unexpectedly ordered to leave Iran three months ago, and that he was picked up by American intelligence operatives during an airport stopover in Amman — details that roughly mesh with what is publicly known about the case.

The account, a translation of which was provided by SITE Intel Group, a nonprofit organization that monitors jihadist Web sites, said authorities in Kuwait had balked at accepting him.

The administration had previously sought to try other senior al-Qaeda operatives, including alleged Sept. 11 mastermind Khalid Sheikh Mohammed, in New York, but backed down in the face of congressional opposition and warnings from New York authorities that the security demands of such a trial would be onerous.

New York Mayor Michael Bloomberg said Friday that he did not believe a trial of Abu Ghaith would present a security risk. “Would I have preferred to have had it elsewhere? I’m not going to get involved in that. I don’t want to make the president’s job any more difficult,” Bloomberg said in his weekly radio interview.

Joby Warrick and William Branigin contributed to this report.