Sen. Rand Paul, R-Ky., is blasting Attorney General Eric Holder's assertion that the government could conceivably use drones against its own citizens in the U.S. as "frightening," saying such an action would violate the Constitution.

Paul was responding to comments by Holder released Tuesday before the Senate Intelligence Committee approved the nomination of John Brennan, President Obama's pick to be his next C.I.A. Director.

Paul said in a statement obtained by Fox News that Holder sent him two letters regarding the constitutionality of the use of legal force such as drones against Americans and on U.S. soil, after Paul petitioned Brennan to speak on the matter.

In the letter, Holder says the U.S. has never carried out a drone strike against one of its citizens on American soil, and calls a situation where such a strike may occur "entirely hypothetical" and "unlikely to occur."

However, Holder does not entirely rule out that such a scenario may occur in the future, and indicates that such a strike would be legal under the Constitution.

“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.

Holder said '"catastrophic" attacks such as the Sept. 11 attacks or the attack on Pearl Harbor are examples of circumstances where the president could conceivably feel such an action is necessary.

Paul says he is not satisfied with the Attorney General's response.

“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,” Paul said.

Paul says he also received a statement from Brennan, who stated that the C.I.A. does not have authority to order such operations be carried out.

Brennan vigorously defended the use of drone strikes during his confirmation hearing. He declined to say whether he believes waterboarding, which simulates drowning, amounted to torture. But he called the practice "reprehensible" and said it should never be done again. Obama ordered waterboarding banned shortly after taking office.

Drone strikes are employed only as a "last resort," Brennan told the committee. But he also said he had no qualms about going after U.S.-born cleric Anwar al-Awlaki in September 2011.

A drone strike in Yemen killed al-Awlaki and Samir Khan, both U.S. citizens. A drone strike two weeks later killed al-Awlaki's 16-year-old son, a Denver native.

The Associated Press contributed to this report.