WASHINGTON — The promise of the armed drone has always been precision: The United States could kill just the small number of dangerous terrorists it wanted to kill, leaving nearby civilians unharmed.

But the Obama administration’s unprecedented release last week of statistics on counterterrorism strikes underscored how much more complicated the results of the drone program have been.

It showed that even inside the government, there is no certainty about whom it has killed. And it highlighted the skepticism with which official American claims on targeted killing are viewed by human rights groups and independent experts, including those who believe the strikes have eliminated some very dangerous people.

“It’s an important step — it’s an acknowledgment that transparency is needed,” said Rachel Stohl, an author of two studies of the drone program and a senior associate at the Stimson Center, a research group in Washington. “But I don’t feel like we have enough information to analyze whether this tactic is working and helping us achieve larger strategic aims.”