WASHINGTON -- Two leading U.S. civil liberties organizations have filed a lawsuit against David Petraeus, Leon Panetta and other senior CIA and military officials over a series of drone strikes in Yemen that killed three American citizens.

The suit, filed Wednesday in Washington and New York by the American Civil Liberties Union and the Center for Constitutional Rights, alleges that the "targeted killing" of the Americans, including suspected al Qaeda operative Anwar al-Awlaki and his teenage son, violated the Constitution because it took place outside the context of authorized armed conflict. The two groups, who filed the suit on behalf of the family members of the dead Americans, are asking the courts to determine for the first time whether the killings were legal.

"While the case is complicated, ultimately it is very simple: our argument is that when the government is killing its own people, it has an obligation to explain it," said Jameel Jaffer, the deputy legal director for the ACLU, in a conference call with reporters Wednesday. "The government has said in response that not only does it not have an obligation to explain it, it doesn't even have to acknowledge it, and we think that is a very dangerous proposition."

Awlaki, a leading propagandist for al Qaeda in the Arab Peninsula, was killed in Yemen in a drone strike in September 2011.

At the time of the strike -- and a subsequent one that killed Awlaki's son -- civil liberties groups questioned whether President Barack Obama had the legal authority to order the killing of someone, particularly an American citizen, in a country with which the U.S. was not formally at war.

In response, the White House has said next to nothing, except to offer indirect rationales for its internal deliberation process, and off-the-record assurances that the president was not violating the Constitution.

The New York Times later detailed how Awlaki became one of several figures on a top-secret presidential "kill list" -- people who Obama has authorized for targeted assassination for their suspected role in terrorism plots. White House officials also told the Times that in assessing civilian casualties from the killings, they assume that anyone in the area of a strike is a combatant until proven otherwise.

The ACLU and the Center for Constitutional Rights both have long track records of attempting to use the courts to force the White House to address the practice of targeted killings across the world, to little avail. In 2010, the two groups sued the government, on behalf of Awlaki's father to prevent his assassination. A judge later threw out the case, ruling that Awlaki's father did not have standing to sue, and asserting that the courts may not have the capacity to assess the decision to place someone on a classified kill list.

The Obama administration has successfully blocked previous efforts by courts to review documents related to the drone assassination program under the state secrets privilege, which permits the executive branch to prevent the review of certain information that could harm national security. The administration declined to acknowledge the existence of the drone program until Obama defended it during a video chat with the public on Google+ earlier this year.

"I think that there's a perception somehow that we're just sending in a whole bunch of strikes willy-nilly," the president said at the time. "This is a targeted, focused effort at people who are on a list of active terrorists who are trying to go in and harm Americans."

The civil liberties groups said on the call Wednesday that they hope the public acknowledgement of the program by government officials means that the state secrets argument may not have relevance in this case.

CORRECTION: The headline of this story originally stated that the civil liberties groups sued the White House instead of the Pentagon.