Three U.S. drone strikes in Pakistan over the weekend killed a total of 27 people, including 9 suspected militants and at least one civilian on Sunday when a drone fired missiles "into a gathering mourning one of two fighters killed in a similar attack the previous day," as reported by AP in Islamabad.

And Monday's strike killed its primary target — top al Qaeda strategist Abu Yahya al Libi.

The weekend strikes highlight the controversy of President Obama's drone program: the killing of al-Qaeda's second-in-command is considered the biggest blow to al Qaeda since U.S. special forces killed Osama bin Laden but the targeting of funeral sites has led to undeniable civilian casualties.

In late January President Obama defended the drone program by saying that "drones have not caused a huge number of civilian casualties" as the strikes are "a targeted, focused effort at people who are on a list of active terrorists, who are trying to go in and harm Americans."

An investigation by the Bureau of Investigative Journalism (BIJ), based on eyewitness accounts and independently sourced evidence, found that between 282 and 535 civilians (including more than 60 children) have been credibly reported as killed in the 275 drones strikes in Pakistan since Obama took office. (There have been eight strikes in the last two weeks).

Furthermore, BIJ found that "CIA’s drone campaign in Pakistan has killed dozens of civilians who had gone to help rescue victims or were attending funerals."

At least 50 of those civilians were killed in follow-up strikes when they had gone to help victims while more than 20 have been attacked in deliberate strikes on funerals and mourners.

The first report of U.S. drones targeting civilians actually came in May 2009 when a drone killed at least 60 people at a funeral for a Taliban fighter in South Waziristan. BIJ notes that over the next two years at least fifteen attacks on rescuers occurred and were reported by the The New York Times, CNN, AP, ABC News and Al Jazeera.

Naz Modirzadeh, Associate Director of the Program on Humanitarian Policy and Conflict Research (HPCR) at Harvard University, told BIJ that killing people at a rescue site has no legal justification:

‘Not to mince words here, if it is not in a situation of armed conflict, unless it falls into the very narrow area of imminent threat then it is an extra-judicial execution’, she said. ‘We don’t even need to get to the nuance of who’s who, and are people there for rescue or not. Because each death is illegal. Each death is a murder in that case.’

The notion that the U.S. is bombing rescue sites and/or funerals is particularly disconcerting because it is usually considered to be a brutal tactic of the Taliban or al-Qaeda and, as legal author Glenn Greenwald points out, the follow-up strike or "double-tap" has been formally denounced as terrorism by the FBI, Department of Homeland Security, the Department of Justice and federal courts.

President Obama's method for counting civilian casualties involves considering "all military-age males in a strike zone as combatants ... unless there is explicit intelligence posthumously proving them innocent," and the CIA doesn't release much information on the secretive program.

In May White House counterterrorism adviser John Brennan said that America is "in an armed conflict with al Qaeda, the Taliban and associated forces, in response to the 9/11 attacks" and that there is nothing in international law that "bans the use of remotely piloted aircraft for this purpose or that prohibits us from using lethal force against our enemies outside of an active battlefield, at least when the country involved consents or is unable or unwilling to take action against the threat."

So if drone strikes eliminate scores of "militants" but each one also kills at least 1-2 civilians (who are surely unable to "take action against the threat"), is it a legally and/or ethically defensible policy?