WASHINGTON — The American Civil Liberties Union and the Center for Constitutional Rights filed a federal lawsuit Monday challenging the U.S. government’s authority to target and kill U.S. citizens outside of war zones when they are suspected of involvement in terrorism.

The civil liberties groups sued in U.S. District Court in Washington after being retained by the father of Anwar al-Aulaqi, a radical U.S.-born cleric who is hiding in Yemen.

The CIA placed al-Aulaqi on its list of suspected terrorists it is authorized to kill earlier this year; the cleric had been on a separate list of individuals targeted by the Joint Special Operations Command.

“The United States cannot simply execute people, including its own citizens, anywhere in the world based on its own say-so,” Vince Warren, executive director of the Center for Constitutional Rights, said in a written statement.

The groups said that the Constitution prohibits targeted killings absent a trial and due process, except as a last resort to prevent specific and imminent threats of death or serious injury.

The groups are seeking a preliminary injunction to halt the U.S. practice of targeting American citizens. They also asked the court to order the government to disclose the standards under which it places individuals, including U.S. citizens, on target lists, noting that it remains unknown how many Americans or other people are on such lists.

“Whatever people think about the merits of the program, we think at a minimum Americans have a right to know under what circumstances the government has the right to impose the death penalty without charge or trial,” said Jameel Jaffer, director of the ACLU’s National Security Project.

The public response to the Obama administration’s extrajudicial targeting of terrorism suspects has so far been relatively muted, unlike the controversy generated by the Bush administration’s efforts to detain enemy combatants without charges or trials.

But Jaffer said that both policies illustrate the ways in which the fight against al-Qaida – which the government has said has no boundaries – threatens to undermine human rights.