The FBI and NYPD grew alarmed that Zazi and his possible co-conspirators might be planning an imminent attack when they found backpacks and cell phones in an apartment.

They also learned that Afzali and other Zazi associates tried to rent a 26-foot U-Haul truck the day before Zazi arrived in Queens.

"The FBI is investigating several individuals in the United States, Pakistan and elsewhere, relating to a plot to detonate improvised explosive devices in the United States," the Justice Department revealed Sunday.

Najibullah Zazi, whose high-profile 28 hours of voluntary questioning last week by prosecutors in Denver broke off suddenly on Saturday, told probers he was trained by Al Qaeda in August 2008 at a camp in Pakistan's Federally Administered Tribal Areas, the government charged.

A laptop found in Zazi's rental car, which the NYPD seized last weekend, contained images of handwritten bomb-making notes, the FBI said. Zazi e-mailed the notes to himself using an account . .

. . named for an 18th century Afghan executed for trying to assassinate a Pashtun tribal leader.

Afzali - who has been an informant for the NYPD in the past, the government said - is accused of tipping off the Zazis that they were under FBI surveillance and then lying about it to investigators.

Afzali, an imam at Masjid Hazart Abubakr Islamic Center on 33rd Ave., told the News just hours before he was arrested that “someone is trying to set me up.”

With Mike Jaccarino