Nafis told an FBI informer in July that he had overseas connections to Al Qaeda, accord­ing to a criminal complaint unsealed Wednesday in US District Court in Brooklyn.

But the plot, which began ­after the accused man, Quazi Mohammad Rezwanul Ahsan Nafis, came to the United States in January, unfolded under the surveillance of the FBI and the New York Police Department as part of an elaborate sting operation, according to court papers.

NEW YORK — Federal prosecutors accused a 21-year-old Bangladeshi man Wednesday of conspiring to blow up the Federal Reserve Bank of New York, saying that he tried to detonate what he believed was a 1,000-pound bomb in a van he parked outside the building in Lower Manhattan.


Nafis, the complaint said, had been trying to recruit people to form a terrorist cell and sought out Al Qaeda contacts to help carry out an attack. One of those he tried to recruit was the FBI informer, who later introduced him to an FBI under­cover agent, the complaint said.

‘‘The defendant came to this country intent on conducting a terrorist attack on US soil and worked with singleminded deter­mination to carry out his plan,’’ said Loretta E. Lynch, US attorney in Brooklyn, who ­unveiled charges along with FBI and New York police officials. ‘‘The defendant thought he was striking a blow to the American economy. He thought he was directing confederates and fellow believers. At every turn, he was wrong, and his exten­sive efforts to strike at the heart of the nation’s financial system were foiled by effective law enforcement.’’

Nafis was charged with conspiring to use weapons of mass destruction and providing ­material support to Al Qaeda; he could face up to life in prison if convicted.

The undercover agent supplied Nafis with 20 50-pound bags of what Nafis believed to be explosives but which were, in fact, inert, the complaint said.