David Coleman Headley, 49, and Tahawwur Hussain Rana, 48, were charged in separate complaints filed Tuesday in U.S. District Court in Chicago.
Prosecutors said Headley traveled to Denmark to identify potential targets for a terrorist attack and that Rana helped arrange Headley's travel.
Headley is charged with conspiracy to commit terrorist acts involving murder and maiming outside the United States. He could be sentenced to life in prison if convicted. He was arrested Oct. 3 at O'Hare International Airport as he boarded a flight to Philadelphia, the first leg of a trip to Pakistan.
Headley and Rana are each charged with conspiracy to provide material support to a foreign terrorism conspiracy, which carries a maximum sentence of 15 years in prison. Rana was arrested Oct. 18 in his home.
Prosecutors said Headley, a U.S. citizen who changed his name from Daood Gilani in 2006, identified and conducted surveillance of potential targets of a terrorist attack in Denmark on two separate trips to that country in January and June. They said Headley reported and attempted to report on his efforts to individuals with ties to terrorism overseas, including at least one with links to al-Qaida.
U.S. Attorney Patrick J. Fitzgerald said in a statement that "the public should be assured that there was no imminent danger in the Chicago area."
"However, law enforcement has a duty to be vigilant to guard against not just those who would carry out attacks here on our soil but those who plot on our soil to help carry out violent attacks overseas," Fitzgerald said.
The Jylands-Posten newspaper published twelve cartoons depicting the prophet Mohammed in 2005, triggering widespread protests throughout the Islamic world and threats from extremist groups.
One cartoon showed Mohammed wearing a bomb-shaped turban. Any depiction of the prophet, even a favorable one, is frowned on by Islamic law as likely to lead to idolatry.