Homeland Security Secretary Janet Napolitano also voiced reservations about the new state law, saying it could siphon federal money and staff from hunting down dangerous immigrants.
The critical comments by the nation's top law enforcement official and the Cabinet secretary responsible for enforcing immigration laws came four days after Arizona's governor signed a law designed to crack down on illegal aliens.
Arizona's new law is, "I fear, subject to potential abuse," Holder told a news conference.
The law allows police to question anyone about their immigration status if they have reason to suspect they are in the country illegally, and makes it a state crime if they are.
