WASHINGTON (Reuters) - A U.S. report on the number of civilian casualties from American counterterrorism strikes will be issued later on Friday, White House spokesman Josh Earnest told reporters.

President Barack Obama has long promised to increase transparency about his administration's use of drones. His administration said in March it would publicly release an assessment of combatant and noncombatant casualties from U.S. counterterrorism strikes in areas outside active war zones since 2009.

The drone campaign has come under criticism by human rights groups and others who say the strikes in Pakistan, Yemen, Somalia and Libya have caused civilian casualties.

Human rights groups, which accuse the Obama administration of not being forthcoming about the precise guidelines that govern drone strikes, have welcomed the expected report amid their calls for greater transparency about the impact from such strikes.

(Reporting by Susan Heavey; Writing by Mohammad Zargham; Editing by Jonathan Oatis)