President Barack Obama has the legal authority to unleash deadly force—such as drone strikes—against Americans on U.S. soil without first putting them on trial, Attorney General Eric Holder wrote in a letter released Tuesday.

But Holder, writing to Republican Sen. Rand Paul of Kentucky, underlined that Obama “has no intention” of targeting his fellow citizens with unmanned aerial vehicles and would do so only if facing “an extraordinary circumstance.”

Paul had asked the Obama administration on Feb. 20 whether the president "has the power to authorize lethal force, such as a drone strike, against a U.S. citizen on U.S. soil and without trial." On Tuesday, he denounced Holder's response as “frightening” and “an affront to the Constitutional due process rights of all Americans.”

“The U.S. government has not carried out drone strikes in the United States and has no intention of doing so,” Holder assured Paul in the March 4, 2013 letter. The attorney general also underlined that “we reject the use of military force where well-established law enforcement authorities in this country provide the best means for incapacitating a terrorist threat.”

Holder added: “The question you have posed is therefore entirely hypothetical, unlikely to occur, and one we hope no President will ever have to confront."

But "it is possible, I suppose to imagine an extraordinary circumstance in which it would be necessary and appropriate under the Constitution and applicable laws of the United States for the President to authorize the military to use lethal force within the territory of the United States," Holder said. "For example, the President could conceivably have no choice but to authorize the military to use such force if necessary to protect the homeland in the circumstances of a catastrophic attack” like Pearl Harbor or 9/11.

“Were such an emergency to arise, I would examine the particular facts and circumstances before advising the President on the scope of this authority,” said Holder.

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Paul, whose office released the letter, denounced the attorney general’s comments.

"The U.S. Attorney General's refusal to rule out the possibility of drone strikes on American citizens and on American soil is more than frightening—it is an affront the Constitutional due process rights of all Americans," the senator said in a statement.

The exchange came as the White House agreed to give Senate Intelligence Committee members access to all of the Justice Department's Office of Legal Counsel opinions justifying Obama's expanded campaign of targeted assassination of suspected terrorists overseas, including American citizens. Some lawmakers had warned they would try to block top Obama counterterrorism adviser John Brennan's nomination to head the CIA unless they were able to see the memos.

A few hours after the White House agreed to share the information, the committee approved Brennan 12-3, setting the stage for a full Senate vote.

Obama's drone war—relatively popular at home, reviled across the Muslim world—has drawn fresh scrutiny ever since NBC News obtained and published a Justice Department memo that lays out the legal justification behind it. The White House has defended the policy as “necessary,” “ethical” and “wise.” But civil liberties champions have sharply criticized it.