Tom Parker, policy director for terrorism and counterterrorism at Amnesty international, says the U.S. needs to be careful because its rationale for the use of drones could be abused by others. For example, the Chinese could use it to go after people it considers a national security threat — maybe Uighur or Tibetan activists living in a third country, he says.

There is "absolutely nothing stopping them from using the same justification," he said. "And, of course, terrorism is often in the eye of the beholder. You're going to see states use this justification to carry out attacks on human rights activists and political opponents."