What’s happening in Iraq and Syria right now is an armed conflict, Hayden said, and targeting is undertaken in compliance with the international law of war. The law of war requires militaries to take precautions to avoid killing noncombatants, but it does not hold them to a near-certainty standard.
After the near-certainty standard was imposed on drone strikes in Pakistan and Yemen, the frequency of strikes dropped precipitously, and the use of so-called signature strikes — attacks aimed at large groups of armed men who fit the profile of militants but whose names were not all known to the CIA — was curtailed. There have been just nine drone strikes in Pakistan this year, according to Long War Journal, a website that tracks the strikes based on media reports. That is down from a high of 110 strikes in 2010. The Bureau of Investigative Journalism, a London-based group that has been critical of drone strikes, found no instance of civilian casualties in Pakistan in 2013 after the policy took effect.
The Syrian Observatory for Human Rights, which opposes the Syrian government, says U.S. airstrikes have killed up to 19 civilians, including several when bombs hit a grain silo Sunday in the town of Manbij.
In Iraq, according to a report in by the National Iraqi News Agency, four civilians were killed in a U.S. airstrikeSept. 26 in Mosul.
Pentagon spokesman Col. Steve Warren said this week that the U.S was investigating the reports of civilian casualties but that, so far, "we’ve found nothing to corroborate" that civilians have been killed.
The U.S. has relied on intelligence-gathering technology — or ISR, which stands for "intelligence, surveillance and reconnaissance" — such as satellites, drones and overhead surveillance flights to determine whether there have been civilian casualties. Few if any human spotters are believed to be on the ground assessing the results of U.S. and coalition airstrikes.
Warren acknowledged that the Pentagon could not say for sure that every person killed in the bombing of Iraq and Syria has been a combatant.
"The evidence is going to be inconclusive often," he said. "Remember, we’re using ISR to determine the battle damage assessment."
Jennifer Cafarella, the top Syria analyst with the Institute for the Study of War in Washington, said the Syrian Observatory reports are generally regarded as credible.
"I think it is likely," she said, "that airstrikes will inevitably result in some civilian casualties."