A grim-faced and apologetic President Obama announced Thursday that two CIA drone strikes on al Qaeda compounds had accidentally killed captive American aid worker Warren Weinstein, an Italian hostage, and two terrorists who were U.S. citizens.
The al Qaeda casualties were Adam Gadahn, a Californian who became a prominent propagandist for al Qaeda, was close to Osama bin Laden and had a $1 million bounty on his head for treason, and Ahmed Farouq, who was described as a deputy commander in Pakistan
The four deaths bring to seven the number of Americans killed in drone strikes in the last five years; only one of them was actually targeted.
When the CIA ordered the strikes on compounds near the Pakistan-Afghanistan border on Jan. 14 and Jan. 19, they were aiming to take out senior al Qaeda leaders, a U.S. official told NBC News. The agency was unaware that Weinstein, Italian hostage Giovanni Lo Porto, Gadahn or Farouq were present, officials said.
In a statement from the White House briefing room, President Barack Obama apologized to the hostages' families and said he took full responsibility as commander in chief.
"As a husband and as a father, I cannot begin to imagine the anguish the Weinstein and Lo Porto families are enduring today," Obama said. "I know there is nothing I can ever say or do to ease their heartache."
Weinstein, 73, was taken hostage in 2011, four days before his seven-year stint with the U.S. Agency for International Development was due to end. Lo Porto was abducted in 2012, soon after arriving in Pakistan to do humanitarian work.
The American, a grandfather from Maryland, had made several video appeals asking Obama to negotiate his release as his health deteriorated.
Weinstein's widow, Elaine, said the family is "devastated" and wished the U.S. and Pakistani governments "with the power to take action and secure his release would have done everything possible to do so."
"There are no words to do justice to the disappointment and heartbreak we are going through," she said, adding that the family is anxious for the results of the U.S. investigation into the operation.
The hostages were "hidden" at an al Qaeda compound unbeknownst to CIA officials who ordered the drone strike after surveillance, Obama said.
U.S. officials told NBC News that the hostages were killed in a controversial tactic known as a signature strike — when the CIA attacks based on a pattern of behavior of people on the ground, even if it doesn't know who it's targeting.
"Sometimes you may not see the al Qaeda leader but there was demonstrated al Qaeda behavior consistent with the presence of a senior Al Qaeda person," the U.S. official said.
The hostages and Farouq were killed in the first drone attack. Gadahn, who was also known as Adam Pearlman and by the nom de guerre Azzam al-Amriki, died in the second.
Gadahn, who converted to Islam in the '90s, moved to Pakistan and became an al Qaeda translator. His profile rose after the death of bin Laden, when it was discovered he regularly corresponded with the terror boss. The State Department had offered a $1 million reward for information leading to his capture.
The details of the strikes were declassified at Obama's direction, the White House said. Senior U.S. officials told NBC News that "cellphone chatter and human intelligence" developed shortly after the airstrikes suggested the hostages may have been killed but that was not confirmed until April.
Obama spoke to Weinstein's widow and the Italian government on Wednesday before making the news public on Thursday.
"He takes full responsibility for these operations and believes it is important to provide the American people with as much information as possible about our counterterrorism operations, particularly when they take the lives of fellow citizens," the White House said in a statement.
"The uniquely tragic nature of the operation that resulted in the deaths of two innocent hostages is something we will do our utmost to ensure is not repeated.
"To this end, although the operation was lawful and conducted consistent with our counterterrorism policies, we are conducting a thorough independent review to understand fully what happened and how we can prevent this type of tragic incident in the future."
Although this is the first case of a U.S. hostage being killed by a drone strike, they have killed four other Americans since 2009. Only one of those, jihadist cleric Anwar al-Awlaki, was targeted.
The American Civil Liberties Union said Thursday's revelation raised "troubling questions about the reliability of the intelligence that the government is relying on to justify drone strikes.
"In each of the operations acknowledged today, the U.S. quite literally didn't know who it was killing," ACLU Deputy Legal Director Jameel Jaffer said.
NBC News' Kelly O'Donnell, Matthew Cole, and Cassandra Vinograd contributed to this report.