United States President Barack Obama will formally nominate a former senior Bush administration official on Friday to head the Federal Bureau of Investigation, the White House said.

Jim Comey, the number two attorney general under George W. Bush, would replace Robert Mueller and serve a 10-year tenure. Mueller has held the job since the week before the terrorist attacks of Sept 11, 2001.

Mueller is set to resign on Sept 4 after overseeing the bureau's transformation into one of the country's chief weapons against terrorism.

The White House said in a statement that Obama would announce his choice of Comey on Friday afternoon.

In the statement, the White House hailed Comey as "one of our nation's most skilled and respected national security and law enforcement professionals".

If confirmed by the Senate, the Republican would take up his new role amid controversy over vast National Security Agency surveillance programs that came to light earlier this month after a government contractor leaked details of them to the media.

The White House may hope that Comey's Republican background and strong credentials will help him through Senate confirmation at a time when some of Obama's nominees have been facing tough battles.

The FBI is responsible for both intelligence and law enforcement, with more than 36,000 employees. It has faced questions in recent weeks over media leak probes involving The Associated Press and Fox News; the Boston Marathon bombings; the attack at Benghazi, Libya, that killed four US citizens; and two vast government surveillance programs into phone records and online communications.

The leaker of those NSA programs, former NSA contractor Edward Snowden, also is the subject of an ongoing criminal investigation.

Just this week Mueller revealed the FBI uses drones for surveillance of stationary subjects and said the privacy implications of such operations are worthy of debate.

Comey, 52, served as deputy US attorney-general for Bush. He had previously been the US attorney for the Southern District of New York.

As assistant US attorney for the Eastern District of Virginia, Comey handled the Khobar Towers bombing case, which arose out of an attack on a US military facility in Saudi Arabia in 1996. Seventeen US military members died in the attack.

Comey gained notoriety for refusing in 2004 to certify the legal aspects of NSA domestic surveillance during a stint as acting attorney-general while John Ashcroft was hospitalized.

After leaving the Justice Department in 2005, he became general counsel to aerospace giant Lockheed Martin Corp until 2010.

He most recently joined Columbia University's law school as a senior research scholar after working for Bridgewater Associates, an investment fund, from 2010 to 2013.

AFP-AP-Reuters