Najibullah Zazi appears in Brooklyn Federal Court in New York on Tuesday, as seen in this courtroom sketch. (Elizabeth Williams/Associated Press)

An Afghan immigrant pleaded not guilty Tuesday to charges of conspiracy to use weapons of mass destruction in connection with a plot to attack New York City transit using common chemicals.

Najibullah Zazi's lawyer entered the plea in a Brooklyn courtroom. Prosecutors accuse Zazi of receiving explosives training from al-Qaeda in Pakistan and they allege he played a direct role in a plan to make and detonate hydrogen peroxide-based bombs on New York City commuter trains, possibly to coincide with the anniversary of the Sept. 11, 2001, hijackings.

U.S. authorities said Zazi had at least three accomplices, although their whereabouts and the extent of their alleged involvement have not been revealed.

"The conspiracy here is international in scope," Assistant U.S. Attorney Jeffrey Knox said in court.

Zazi and his co-conspirators bought beauty products in Colorado containing hydrogen peroxide and acetone, which are key ingredients for homemade bombs, officials allege.

Handwriting and fingerprints appearing to match Zazi's were found on materials — batteries and a scale — that could be used to make explosives, prosecutors said.

Zazi, 24, an airport van driver and former coffee cart vendor, has denied any wrongdoing. He told the FBI that he must have unintentionally downloaded the notes as part of a religious book and that he deleted the book "after realizing that its contents discussed jihad."

Zazi is also charged, along with two other men, with lying to authorities in a continuing terror investigation.

The other two are his father, Mohammed Wali Zazi, and Ahmad Wais Afzali, an imam at a mosque in the New York City borough of Queens.

Last week, U.S. prosecutors told a federal court in Denver that Zazi made at least two trips to Canada, raising concern he might have tried to organize another terror cell north of the border.

However, Zazi's family members told CBC News that he was just visiting his dying grandmother in Mississauga, Ont.

Canadian officials haven't commented on the allegation of Zazi's cross-border visits. A spokesman for Public Safety Minister Peter Van Loan would only say Canada monitors national security concerns and is vigilant in protecting against any terrorist threats.

With files from The Associated Press