Police in Oregon and Michigan have arrested six people on charges that they conspired to wage war on the US and provide support to al Qaeda.
Attorney General John Ashcroft announced the arrests at a Justice Department news conference.
He called it a "defining day" in the fight against terrorism adding that one of them had US military training.
Court records say the men travelled to Afghanistan for training.
Mr Ashcroft says the arrests represent "a textbook example" of cooperation among federal, state and local authorities in the war against terrorism.
Court papers identified the six men as Jeffrey Leon Battle, Patrice Lumumba Ford, Ahmed Ibrahim Bilal, Muhammad Ibrahim Bilal, Habis Abdullah al Saoub and October Martinique Lewis.
According to the Attorney General, Battle was a former US soldier.
FBI Director Robert Mueller says that "those who support terrorism or acts of terrorism will be brought to justice".
John Ashcroft said some of the men began travelling to Afghanistan in October 2001 to fight with Taliban troops against US forces.
A federal grand jury has indicted the men on charges of conspiracy to levy war against the US, conspiracy to provide material support and resources to al Qaeda, conspiracy to contribute services to al Qaeda and the Taliban and possessing firearms in furtherance of crimes of violence.
PA