Outgoing Federal Bureau of Investigation Director Robert Mueller is late in responding to Kentucky Republican Senator Rand Paul’s inquiry about FBI surveillance drone use, prompting the top U.S. lawmaker to threaten to block the Senate confirmation of Mueller’s replacement.

After hearing only silence from Mueller on the FBI’s use of domestic surveillance drones eight days past the junior Kentucky senator’s July 1 deadline, Paul threatened to block the Senate confirmation of James Comey as the new head of the Federal Bureau of Investigation.

Firing off a letter to Mueller on Tuesday, Paul said, “Unfortunately, I have not received any answers to my questions, and I have not been informed as to when I should expect a reply.”

On Tuesday, the Senate Judiciary Committee questioned Comey — who is President Obama’s top pick for the position — over his positions on torture, the Boston Marathon Bombings and the federal government’s surveillance apparatus.

Paul notes in his letter that the full Senate could take up consideration of Comey’s confirmation later in the month.

Mueller — whose term officially expires on September 4 after 12 years of service — admitted to the heads of the Senate Judiciary Committee on June 19 that the bureau uses drones for domestic surveillance purposes, but their use was “very seldom.”

Paul, not happy with the Mueller’s silence on the issue, declared in his recent letter — which was a followup to one sent on June 20 — that “legitimate questions on important government functions should not be ignored.”

“These questions are easily answerable and primarily questions of fact, so I respectfully request again that you provide answers to these questions,” said Paul.

“As you know, the President has submitted the nomination of your successor to the Senate, the Senate Judiciary Committee has begun consideration of his nomination, and that nomination could be considered by the full Senate this month,” he said.

“Without adequate answers to my questions, I will object to the consideration of that nomination and ask my colleagues to do the same,” he said.

Paul famously filibustered the Senate confirmation of CIA Director John Brennan with the help of Republican Senators Ted Cruz and Mike Lee on March 6, demanding clarification from the Obama administration over its policy on domestic drone use and the targeted assassinations of Americans on U.S. soil.

Drones, formally called unmanned aerial systems, have been a source of controversy since Obama signed into law the integration of drones into domestic airspace.

The FAA was scheduled to begin the integration of “safe” governmental and non-government drones into domestic airspace in August 2012.

Paul’s filibuster, which lasted almost 13 hours, generated over a million Tweets, forcing other Republican lawmakers to take notice and run back from a dinner with the White House to make sure they were seen supporting Paul.

Attorney General Eric Holder, after having given Congress soft and ambiguous answers on the subject, answered Paul, stating that the President does not have the authority “to use a weaponized drone to kill an American not engaged in combat on American soil.”

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