Najibullah Zazi, seen in Denver on Sept. 17, is charged with conspiring to explode bombs in the United States. (Ed Andrieski/Associated Press)

An Afghan-born Colorado man charged with conspiring to explode bombs in the United States made several trips to Canada, U.S. authorities said Friday.

U.S. prosecutors told a federal court in Denver the travels of Najibullah Zazi across the border raise concern he might have tried to organize another terror cell north of the border.

While the surprise revelation by prosecutors is raising concerns in U.S. intelligence circles, a family member has told CBC News that Zazi was just visiting his dying grandmother in Mississauga, Ont.

U.S. prosecutor Tim Neff told the court that Zazi played a direct role in a plan to make and detonate hydrogen peroxide-based bombs on commuter trains, possibly to coincide with the anniversary of the Sept. 11, 2001, hijackings.

"The evidence suggests a chilling, disturbing sequence of events showing the defendant was intent on making a bomb and being in New York on 9/11, for purposes of perhaps using such items," Neff said.

Zazi, a 24-year-old Colorado airport shuttle driver and coffee cart owner in New York, was transferred on Friday on the orders of U.S. Magistrate Judge Craig Shaffer from Denver to New York City to face charges of conspiracy to use weapons of mass destruction.

Zazi is due to make an appearance in court in Brooklyn on Tuesday.

Investigators said they found notes on bomb-making that appear to match Zazi's handwriting and discovered his fingerprints on materials — batteries and a scale — that could be used to make explosives.

Zazi 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, 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.

With files from The Associated Press