WASHINGTON — An investigation of American drone strikes in Yemen concludes that the Obama administration has not followed its own rules to avoid civilian casualties and is setting a dangerous example for other countries that want to use unmanned aircraft against terrorists.

The study, by the Open Society Justice Initiative, a legal advocacy group based in New York, was released on Monday at a time when Yemen has been engulfed in violence and American drone strikes have been slowed or halted. But its observations about the performance of American counterterrorism strikes from 2012 to 2014 remain relevant for assessing a novel weapons system that the United States has used in several countries and has now approved for export to a limited number of allies.

Despite promises of greater openness about drone strikes, the Obama administration has continued to guard their secrecy closely and says nothing publicly about strike targets and results. The resulting information vacuum has been partly filled by independent studies by groups like the Open Society Justice Initiative, which worked with the Mwatana Organization for Human Rights, a Yemeni group that interviewed witnesses.

In May 2013, in a long-planned speech on the targeted killing of terrorists, President Obama described a rigorous standard that he said guided all drone strikes. “Before any strike is taken, there must be near-certainty that no civilians will be killed or injured — the highest standard we can set,” he said.