A U.S. counterterrorism drone strike killed two hostages taken by al-Qaeda, the White House announced Thursday. It also said it believes two American leaders of the terror group, including al-Qaeda spokesman Adam Gadahn, have been killed.
The hostages killed were American Dr. Warren Weinstein and Italian national Giovanni Lo Porto, according to a White House statement, which said the strike took place in January.
At the White House, President Barack Obama expressed his condolences to the families of Weinstein and Lo Porto, who were serving as aid workers in Pakistan before being taken hostage, who had been held since 2011 and 201, respectively.
Read More Military: One system, many drones
"I realize that there are no words that can ever equal their loss, I know that there is nothing that I can ever say or do to ease their heartache," Obama said, "And today I simply want to say this: As president and commander in chief I take full responsibility for all our counterterrorism operations. ... I profoundly regret what happened."
The president said U.S. forces did not know that al-Qaeda had hid the two hostages in the compound they planned to target with counterterror operations. "It is a cruel and bitter truth that in the fog of war, generally, and in our fight against terrorists specifically, mistakes—sometimes deadly mistakes—can occur," Obama said.
The announcement also said that two other Americans, working for al-Qaeda, were likely killed in U.S. counterterror operations in the same region along the Afghanistan-Pakistan border. The White House said "neither was specifically targeted, and we did not have information indicating their presence at the sites of these operations."
Ahmed Farouq—an American al-Qaeda leader—died in the January operation that killed the two hostages, the statement said.
The White House said it concluded that a separate operation killed Gadahn, a prominent member of the terror group that carried out the Sept. 11, 2001, attacks. Gadahn, who was born in Oregon and converted to Islam in California, was a spokesman and cultural interpreter for al-Qaeda.
"The President directed that the information being shared today, which was properly classified until now, be declassified and shared with the American people," the statement said. "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 president said he declassified the incidents because the U.S. "is a democracy committed to openness in good times and in bad."
The White House said the operation that resulted in hostages' deaths "was lawful and conducted consistent with our counterterrorism policies" but added that an independent review is underway "to understand fully what happened."
"We will identify the lessons that can be learned from this tragedy and any changes that should be made," Obama said.
—The Associated Press contributed to this report.