It alleged that he diverted $1.5 million in donations by the Taiwanese government from a programme called "Libraries for Peace" to accounts controlled by family and friends in the US and elsewhere.
He has denied the charges.
Following his arrest, Portillo told Guatemala's Radio Sonora that he was the victim of a conspiracy that began before he took office and that he feared for his life, the AFP news agency reported.
"When I am in court, I'll mention all the names of the people behind the conspiracy"
Alfonso Portillo, former Guatemalan president
"When I am in court, I'll mention all the names of the people behind the conspiracy ... everything they've done, where they met," he said in a telephone interview.
"With all they've done to me in Guatemala, anything can happen."
Portillo, who also faces corruption charges at home in Guatemala, won office promising to redistribute wealth.
He fled to Mexico after losing immunity from prosecution when his term ended.
He was extradited from Mexico to Guatemala in 2008 and was free on bail when the US made its extradition request earlier this month.
Telesforo Guerra, Portillo's lawyer, has said he will fight to enforce a 2008 law that requires suspects be tried for charges they face in Guatemala before being extradited.
"We are going to prove that this is a political trial. We have proof," the Associated Press news agency quoted Guerra as telling Radio Sonora.
If found guilty, Portillo faces a maximum prison sentence of 20 years.