WASHINGTON - President Barack Obama will lay out the rationale for US drone strikes in a speech on Thursday, a White House official said.

"He will discuss why the use of drone strikes is necessary, legal, and just, while addressing the various issues raised by our use of targeted action," the official said.

The speech will coincide with the signing of new "Presidential Policy Guidance" to lay out standards for lethal drone strikes, the official said.

Obama will also reiterate his pledge to close the US military prison at Guantanamo Bay, Cuba where foreign terrorism suspects are held and "announce a number of specific steps to advance that goal," the official said.