US authorities have arrested a 24-year-old airport shuttle driver and his father as part of their terrorism investigation in New York and Colorado.
A spokeswoman for Najibullah Zazi's defence team said he and his father were taken into custody at his suburban Denver apartment by FBI agents last night.
It is not yet clear what charges the men may face.
Zazi's father was named as Mohammed Wali Zazi, 53. A third man, Ahmad Wais Afzali, 37 was arrested in New York City on the same charges, the Justice Department said today.
Afzali and the 24-year-old Zazi are legal permanent US residents from Afghanistan, and the elder Zazi is a naturalised US citizen from Afghanistan.
Each was charged with knowingly and wilfully making false statements to the FBI "in a matter involving international and domestic terrorism", the department said in a statement. It emphasised that the timing or location of any planned attack was not known.
The FBI is investigating several individuals in the United States, Pakistan and elsewhere in an alleged plot to detonate explosive devices in the United States, the Justice Department said.
In supporting documents filed with the court, federal investigators said a September 11 search of Zazi's rental car in New York turned up a laptop computer which contained an image of nine pages of handwritten notes, which included formulas and instructions about how to build explosives, detonators and other components of a fusing circuit.
Zazi was asked about the notes during FBI interviews last week and said he knew nothing about them, the documents said.
When asked about the handwritten notes allegedly found on his computer, Zazi said he had not written them and that he must have unintentionally downloaded them along with a religious book he downloaded in August. He said he deleted them within a few days after realising they discussed jihad, the affidavit said.
The FBI's court filings also said Zazi admitted to FBI agents last week that in 2008 he received al-Qaida weapons and explosives training at an al-Qaida training facility in Pakistan, near the border with Afghanistan.
Zazi has repeatedly denied any connection to al-Qaida or to a purported terrorist plot.
Authorities say Zazi rented a car and drove from Denver to New York, crossing into Manhattan on September 10. Zazi said he went to New York to resolve issues with a coffee cart he owns in Manhattan, then flew home to Denver.
On Monday, FBI agents and police officers with search warrants seeking bomb materials searched three apartments and questioned residents in the Queens neighbourhood where Zazi stayed.
A joint FBI-New York Police Department task force feared Zazi may have been involved in a potential plot involving hydrogen peroxide-based explosives like those cited in an intelligence warning issued last Monday.
Zazi's attorney, Art Folsom, denied any such claims.
The Zazis are scheduled to appear in court in Denver tomorrow and Afzali is to appear Monday in court in the Eastern District of New York.
If convicted, each would face eight years in prison.
US Attorney General Eric Holder said the FBI was "working this case around the clock" in New York, Denver and other parts of the country but that there was no imminent threat.