A CIA drone strike in January that was aimed at a suspected al-Qaida compound in Pakistan accidentally killed two hostages, including a kidnapped American, U.S. officials acknowledged yesterday.

U.S. officials said they didn't realize until weeks later that two civilians had died in the attack -- kidnapped aid workers Warren Weinstein of Maryland and Giovanni Lo Porto of Italy -- despite assurances from the CIA at the time of the operation that only al-Qaida fighters were present.

The CIA had been conducting surveillance on the site near the Afghan border for hundreds of hours, U.S. officials said.

But the spy agency later discovered the strike had killed a second U.S. citizen: Ahmed Farouq. U.S. officials said the American had joined al-Qaida years earlier and was among the suspected militants at the compound.

After the CIA pieced together what had happened, the spy agency's director, John Brennan, delivered the news to President Barack Obama last week.

Yesterday, in brief remarks from the White House, a grim and downcast Obama informed the nation of the botched operation.

"As president and as commander in chief, I take full responsibility for all our counterterrorism operations, including the one that inadvertently took the lives of Warren and Giovanni," Obama said. "I profoundly regret what happened. On behalf of the United States government, I offer our deepest apologies to the families."

Weinstein, 73, had been held since 2011 after being kidnapped in Lahore, Pakistan. Lo Porto, 39, had been in al-Qaida captivity since 2012.

Obama said he spoke Wednesday with Weinstein's wife, Elaine, and Italian Prime Minister Matteo Renzi to inform them of the bungled operation.

In a statement, Elaine Weinstein said yesterday that she and her family were devastated by the news and still do not "yet fully understand all of the facts surrounding Warren's death."

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"We were so hopeful that those in the U.S. and Pakistani governments with the power to take action and secure his release would have done everything possible to do so and there are no words to do justice to the disappointment and heartbreak we are going through," she said.

Earnest said the families of the two hostages will receive U.S. government compensation, but declined to provide details.

Obama said the operation was "fully consistent with the guidelines" he has established for counterterrorism strikes against al-Qaida, but that he has ordered "a full review" of what happened.

"It is a cruel and bitter truth that in the fog of war generally and our fight against terrorists specifically, mistakes, sometimes deadly mistakes, can occur," the president added.

Obama did not specify how or where the hostages were killed, or which arm of the U.S. government was responsible.

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A CIA spokesman declined to comment.

Two Pakistani intelligence officials, both of whom spoke on condition of anonymity, said they believe Weinstein, Lo Porto and Farouq were killed during a Jan. 15 drone strike in the Shawal Valley in North Waziristan, part of Pakistan's tribal belt.

Although Obama did not mention it in his remarks, a third American was killed in a separate counterterrorism operation in January, the White House acknowledged in a statement.

Adam Gadahn, 36, a California native who converted to Islam and joined al-Qaida more than a decade ago, was killed in a CIA drone attack in Pakistan within a week of the strike that killed the hostages, U.S. officials said.

Gadahn, who called himself "Azzam the American" and helped run al-Qaida's propaganda department, was indicted by a federal grand jury in 2006 on charges of treason.