The Afghan-born U.S. immigrant accused of plotting a terrorist attack on New York City has pleaded not guilty to the alleged act in a U.S. court.

Najibullah Zazi's lawyer entered the plea in a Brooklyn courtroom on Tuesday morning.

The 24-year-old Zazi was ordered to be held without bail and he remains in custody. He is scheduled to return to court on December 3.

Prosecutors allege that Zazi travelled to Pakistan last year and was trained to make explosives by members of al Qaeda. And they claim that the accused may have intended to target mass transit in the New York City area.

U.S. authorities allege that they have found bomb-making instructions on the Denver airport shuttle driver's computer and they believe he and other accomplices purchased products in Colorado containing ingredients -- hydrogen peroxide and acetone -- that can be used to make bombs.

But Zazi's lawyer says he does not know of anyone who is connected to his client on these same allegations.

"I don't know the names of anybody else that allegedly conspired with Mr. Zazi," J. Michael Dowling said Tuesday. "Those names have not been produced."

Canadian officials have not commented on reports that Zazi made at least two trips north of the U.S. border, though the Globe and Mail has reported that he visited his grandmother in Mississauga, Ont., in recent years.

Investigators have previously indicated in court that they are investigating whether Zazi has any terror ties in Canada.

On Tuesday, Zazi's lawyer, Michael Dowling, entered a plea of not guilty for his client.

Judge Raymond Dearie then ordered Zazi into permanent detention during the trial, saying "there are no reasonable conditions that will ensure this gentleman's presence or the safety of the community."

Dowling later told reporters that his client did travel to Pakistan, and also bought beauty products, but never broke the law in doing so.

He also said prosecutors did not have enough evidence for the conspiracy charges against Zazi -- police allege there were three accomplices in the bomb plot, but only Zazi has been publicly identified.

"The government will have to produce someone else -- they don't necessarily have to indict them -- or the conspiracy charge fails," he said. "You can't convict him of conspiracy without an agreement."

Zazi's next court appearance is scheduled for Dec. 3.

With files from The Associated Press