Three men of Afghan origin including one accused of training with Al-Qaeda have been arrested over a plot to conduct attacks in the United States, officials said on Sunday.
The US Justice Department said the FBI was also investigating other individuals "in the United States, Pakistan and elsewhere, relating to a plot to detonate improvised explosive devices in the United States," according to affidavits filed to support the arrests.
Najibullah Zazi, 24, and his 53-year-old father Mohammed -- both Afghan natives -- were arrested in the western US state of Colorado late Saturday, the department said in a statement. Ahmad Wais Afzali, 37, also from Afghanistan, was later arrested in New York. All three reside legally in the United States.
"Each of the defendants has been charged by criminal complaint with knowingly and willfully making false statements to the FBI in a matter involving international and domestic terrorism," the statement said.
Najibullah Zazi, a permanent US resident, and Mohammed Zazi, a naturalized US citizen, are set to appear in a Colorado federal court on Monday.
On the same day Afzali, also a permanent US resident, stands before a federal court in New York.
If convicted each man faces eight years in prison.
The arrests come after raids this week in New York and Colorado and three days of voluntary questioning of Najibullah Zazi in Denver, Colorado.
"The arrests carried out tonight are part of an ongoing and fast-paced investigation," said David Kris, assistant attorney general for national security.
"It is important to note that we have no specific information regarding the timing, location or target of any planned attack," he added.
But a former FBI counter-terrorism director, Steve Pomerantz, said it appeared the arrests on lying charges provided the FBI with the pretext to detain the suspects while they investigate further.
"There's probably a lot more coming down the road," Pomerantz told Fox television, referring to potential additional charges.
According to US media reports this week, investigators focused on an alleged plot targeting New York, hit in the devastating attacks on September 11, 2001.
The CNN network, citing sources close to the investigation, reported the target was a major New York transportation hub, such as a rail or subway station. Najibullah Zazi, a bus driver in Colorado, possessed a video of New York's Grand Central Station, the network said.
US media also said authorities found 14 new black backpacks in the New York raids that fueled concern the men may have been planning to use them to carry suicide bombs.
And the New York Post reported Sunday that Giants Stadium outside the city was a potential target, and that stadium security officials said the Federal Bureau of Investigation sent them alerts about a possible threat.
Justice Department officials said Sunday they had intercepted a number of phone calls between Najibullah and Mohammed Zazi and Afzali where the defendents discuss Afzali being interviewed by authorities.
Najibullah Zazi told Afzali his car had been stolen and that he feared he was being "watched," according to the affidavits.
Afzali then allegedly asked him whether there was any "evidence in his car," to which Najibullah replied no.
In a search of Najibullah Zazi's rental car in New York, where he had been visiting Afzali, officials said in the affidavits that they found a digital image of handwritten notes "regarding the manufacture and handling of initiating explosives, main explosives charges, explosives detonators and components of a fusing system."
When asked about and shown the notes, Zazi "falsely asserted that he had never seen the document before," officials said.
In interviews with FBI agents in Denver, according to the affidavits, Najibullah Zazi meanwhile admitted that on a 2008 trip to Pakistan he "attended courses and received instruction on weapons and explosives at an Al-Qaeda training facility."
But in a telephone interview with Zazi reported in the Denver Post newspaper on Saturday, he denied admitting any link to Al-Qaeda or involvement in an attack plot.
US Congressman Peter King of New York told Fox he was disturbed by what US agents had uncovered about potential attacks.
"Whenever you talk about someone trained by Al-Qaeda, when you talk about the possibility of explosives... you're talking about something that's very, very serious," King said.