Survivors of three Americans killed by targeted drone attacks in Yemen last year sued top-ranking members of the United States government, alleging Wednesday they illegally killed the three, including a 16-year-old boy, in violation of international human rights law and the U.S. Constitution.

"The government has killed three Americans. It should account for its actions. This case gives us an opportunity to do that," Jameel Jaffer, deputy legal director with the American Civil Liberties Union, said in a press call.

The suit, (.pdf) is being litigated by the Center for Constitutional Rights and the ACLU. It seeks unspecified damages and highlights the government's so-called unmanned "targeted killing" program. The ACLU and the Center maintain the drone attacks have killed thousands, including hundreds of innocent bystanders overseas. (Other estimates of the campaign come to widely different conclusions.)

The suit, the first of its kind, alleges the United States was not engaged in an armed conflict with or within Yemen, prohibiting the use of lethal force unless "at the time it is applied, lethal force is a last resort to protect against a concrete, specific, and imminent threat of death or serious physical injury." The case directly challenges the government's decision to kill Americans without judicial scrutiny.

At bottom, Jaffer said, "the question is whether the government is justified in killing without charging them or trying them for anything."

The suit is brought on behalf of Anwar Al-Awlaki, a radical cleric and a native of New Mexico. He was originally known for his incendiary blog and YouTube videos. But according to the Obama administration, Awlaki's role morphed from marketer to operational planner and recruiter for al-Qaida in the Arabian Peninsula. U.S. authorities claim he had contacts with the 9/11 hijackers, the underwear bomber and others.

He was killed Sept. 30 last year. Also killed was Samir Khan, the editor of the English magazine Inspire, which allegedly was published by Al-Qaida in the Arabian Peninsula.

Two weeks later, the cleric's 16-year-old son, Abdulrahman Al-Awlaki, was killed in a separate Yemen attack.

The defendants include Defense Secretary Leon Panetta, CIA Director David Petraeus, U.S. Navy Adm. William H. McRaven and U.S. Army Maj. Gen. Joseph Votel.

Citing U.S. officials, the Washington Post has reported that the son and Khan were not intended targets.

The Justice Department did not immediately respond for comment. The administration refuses to release the Justice Department memo that legally justifies targeting Americans, and according to the New York Times, President Obama approves or denies who gets added to the "kill list."

But Attorney General Eric Holder said in a March speech at Northwestern University Law School that "Our legal authority is not limited to the battlefields in Afghanistan." He said the legal authority Congress passed following the Sept. 11, 2001 terror attacks covers Yemen and Somalia, where other unmanned drone attacks have been carried out.

Holder said the administration takes action with "the consent of the nation involved or after a determination that the nation is unable or unwilling to deal effectively with a threat to the United States."

In another suit, the ACLU is invoking the Freedom of Information Act seeking details of the government's drone program. In that case, the CIA refuses to confirm or deny the covert military use of drones to kill suspected terrorists overseas.