WASHINGTON — US President Barack Obama announced measures Tuesday allowing civilian investigators to handle cases of terror suspects, effectively sidestepping a 2011 law requiring they be brought before military courts.

The directive provides more flexibility to the president in deciding whether to use military tribunals to try foreign terror suspects, and is likely to upset lawmakers who included the rule in last year's National Defense Authorization Act (NDAA).

"The executive branch must utilize all elements of national power -- including military, intelligence, law enforcement, diplomatic, and economic tools -- to effectively confront the threat posed by Al-Qaeda and its associated forces," Obama wrote in a presidential directive.

The White House, he added, "must retain the flexibility to determine how to apply those tools to the unique facts and circumstances we face in confronting this diverse and evolving threat.

"A rigid, inflexible requirement to place suspected terrorists into military custody would undermine the national security interests of the United States, compromising our ability to collect intelligence and to incapacitate dangerous individuals," he added.

Obama signed the NDAA under protest on December 31 which required that foreign terror suspects affiliated with Al-Qaeda and plotting or conducting attacks on US soil be brought before military courts.

He attached a statement to the bill, saying he signed it "despite having serious reservations with certain provisions that regulate the detention, interrogation, and prosecution of suspected terrorists."

The December law revived debate over the complicated legal thicket surrounding the treatment of terror suspects and over rules hurriedly drawn up by the previous Bush administration after the September 11 attacks in 2001.

Obama has sought to preserve the option of trying some terror suspects in federal courts, or for those accused of plotting new attacks against the United States to be processed through the civilian legal system, and his move Tuesday appeared to solidify that option.

The directive is aimed in part at preventing a disruption of terror investigations conducted by the Federal Bureau of Investigation.