The White House and Justice Department on Tuesday adamantly defended the administration's authority to use unmanned drones to kill terror operatives -- even if those operatives are U.S. citizens -- following the release of a controversial memo on the program.
President Obama's advisers are also trying to tamp down concerns about the targeted killings ahead of the confirmation hearing Thursday for CIA director nominee John Brennan -- the counterterrorism adviser and drone-program supporter who has come under criticism from Democrats.
Pressed repeatedly about the complicated constitutional and legal questions raised by the targeted killing of Americans, White House Press Secretary Jay Carney said Tuesday that the president takes those issues "very seriously."
But he noted that Al Qaeda is in a "state of war against us," and defended what he described as "targeted strikes against specific Al Qaeda terrorists."
"We conduct those strikes because they are necessary to mitigate ongoing actual threats, to stop plots, to prevent future attacks and to save American lives," Carney said. "These strikes are legal, they are ethical and they are wise."
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Carney would not describe the legal criteria for ordering those drone strikes.
A Justice Department official, though, told Fox News there are at least three conditions that have to be met in order for a strike to be ordered -- there has to be an "imminent" threat, the target has to have engaged in terrorist activities, and the target has to be unable to be captured.
Separately, Attorney General Eric Holder said Tuesday that the government is "confident that we're doing so in a way that is consistent with federal and international law."
Under Obama, the U.S. drone program has ramped up dramatically since the George W. Bush administration. It has become one of the most important tools in the administration's counterterrorism campaign -- particularly in Pakistan, but also in the expanding fronts of the war against Al Qaeda and its affiliates.
Scrutiny of the program follows a 2011 drone strike in Yemen that killed two Americans -- Anwar al-Awlaki and Samir Khan. It marked the first time an American citizen was targeted for death by a U.S. president and killed in a drone strike.
On Monday, a bipartisan group of 11 senators wrote a letter to Obama asking for "any and all legal opinions" that describe the basis for the authority to "deliberately kill American citizens."
The questions come in advance of Brennan's confirmation hearing Thursday before the Senate intelligence committee. Several of the authors of the drone letter sit on that committee. Obama's nominee for Defense secretary, Chuck Hagel, also had his confirmation hearing last week. The letter Monday made a blunt threat suggesting that withholding information on drones could imperil those nominations.
"The executive branch's cooperation on this matter will help avoid an unnecessary confrontation that could affect the Senate's consideration of nominees for national security positions," the senators wrote.
As the letter was released, a Justice Department document surfaced in news reports describing the administration's drone-attack authority.
As first reported Monday night by NBC News, the memo says it is legal for the government to kill U.S. citizens abroad if it believes they are senior Al Qaeda leaders continually engaged in operations aimed at killing Americans -- even if there is no intelligence pointing to an active plot against America.
The 16-page document says that delaying action against individuals continually planning to kill Americans would create an unacceptably high risk. It adds that the threat posed by Al Qaeda and its associated forces demands a broader concept of when a person continually planning terror attacks presents an imminent threat.
It's unclear whether that will satisfy lawmakers' concerns. Sen. Dianne Feinstein, D-Calif., chairwoman of the intelligence committee, said in a statement Tuesday that the document was already provided to the committee last year.
"The committee continues to seek the actual legal opinions by the Department of Justice that provide details not outlined in this particular white paper," she said. Feinstein was not among the senators who signed the letter to Obama Monday.
While Awlaki was considered a powerful terror operative for Al Qaeda in the Arabian Peninsula, he was never charged. In their letter Monday, the senators said they believe there are "circumstances" where a U.S. president can use "lethal force" against Americans who "choose to take up arms" against their country, "just as President Lincoln had the authority to direct Union troops to fire upon Confederate forces during the Civil War."
But they said "it is vitally important" for Congress and the public to understand how the administration interprets the limits on that power. They complained that the administration has ignored prior requests for legal opinions from the Justice Department.
Brennan, a vocal supporter of the drone program and other controversial counterterrorism tools dating back to the George W. Bush administration, is facing a level of criticism from Democrats that no other Obama nominee has encountered. Eight Democrats and three Republicans penned the letter to Obama Monday. One of them, Sen. Ron Wyden, D-Ore., has previously pressed Brennan on the drone issue.
Another, Sen. Mark Udall, D-Colo., said last week he was "deeply disappointed" coming out of a meeting with Brennan. He claimed the White House counterterrorism adviser was "unprepared" to discuss a recent report on the CIA detention and interrogation program.
The Associated Press contributed to this report.