Mr Zazi denies any involvement in the alleged plot
An Afghan-born US man has been charged with plotting to carry out bomb attacks on the US.
Najibullah Zazi, 24, was charged by the New York Grand Jury with planning to use "one or more weapons of mass destruction" in the attacks.
US officials have also arrested and charged two other men over offences relating to unconnected bomb plots in Illinois and Texas, reports say.
A federal courthouse was targeted in Illinois, an office block in Dallas.
Najibullah Zazi is alleged to have received bomb-making training in Pakistan.
Ahmad Afzali, an imam arrested along with Mr Zazi, has been charged with lying to investigators and released on $1.5m (£1m) bail.
Mr Afzali, Mr Zazi and Mr Zazi's father, Mohammed, were detained last Saturday - all three deny any involvement in the alleged plot.
Mohammed Zazi had already been released on bail.
In a statement, the US Department of Justice said Mr Zazi had "knowingly and intentionally conspired with others to use one or more weapons of mass destruction, specifically explosive bombs and other similar explosive devices, against persons or property within the United States".
Attorney General Eric Holder said investigators were examining "a wide range of leads" and would "continue to work around the clock to ensure that anyone involved is brought to justice".
He said that officials believed any "imminent threat" from the alleged plot had been disrupted.
The other arrests that follow the Zazi case are unconnected, reports say.
In Dallas Texas, the FBI arrested a 19-year-old Jordanian man who they say was attempting to blow up a skyscraper in the city. Hosam Maher Husein Smadi has been charged with attempting to use a weapon of mass destruction.
The FBI say Smadi had been under constant surveillance and - in relation to an on-going sting operation - a decoy device had been supplied to the suspect by an undercover agent.
The other case relates to 29-year-old Michael Finton, a Muslim convert also known as Talib Islam, who was arrested after attempting to blow up a car bomb outside a courthouse in Springfield, Illinois.
Again, an FBI undercover team had provided fake explosives.
Mr Zazi and his father were arrested in their home city of Denver while the third man, Ahmad Wais Afzali, 37, was arrested in Queens, New York, where he works.
Investigators have told the media that bomb-making instructions were found in Mr Zazi's house in Denver, Colorado, although no explosives have been found.
A legal resident of the US since 1999, Mr Zazi is alleged to have received "detailed" explosives and weapons training at a camp in Pakistan last year.
He is also accused of conducting "extensive" internet research on bomb-making and to have bought the components for building explosive devices.
Court papers allege he tried to communicate with another person on multiple occasions seeking advice on how to correct the ingredients for a bomb mixture, with "each communication more urgent in tone than the last".
But in a recent telephone interview with the Denver Post newspaper Mr Zazi denied the allegations and said he had nothing to hide.
The BBC's Adam Brookes in Washington says investigators will attempt to establish a link between Mr Zazi and Islamist extremists in Pakistan.
If the allegations are proved to be true, it would be the first home-grown US terror plot with direct links to Pakistani extremists, our correspondent says.