Three men are due to appear before a US federal court tomorrow on charges of lying to federal agents about a plot to blow up unspecified targets in the US.
The US Justice Department said the FBI is also investigating other individuals in the US, Pakistan and elsewhere.
The investigation relates to a plot to detonate improvised explosive devices in the US.
Afghan-born Najibullah Zazi, 24, and his 53-year-old father Mohammed were arrested in Colorado yesterday.
Ahmad Wais Afzali, 37, also from Afghanistan, was later arrested in New York.
All three men were expected to make initial court appearances tomorrow in Denver and New York. Each faces a possible eight years in prison if convicted.
'Each of the defendants has been charged by criminal complaint with knowingly and wilfully making false statements to the FBI in a matter involving international and domestic terrorism,' the statement said.
The arrests come after raids this week in New York and Colorado and three days of voluntary questioning of Najibullah Zazi in Denver, Colorado.
Investigators focused in the questioning on an alleged plot targeting a major New York transportation hub, such as a subway station.
