President Barack Obama has revealed an American and an Italian hostage were killed in a covert US counter-terrorism operation on the Afghan-Pakistan border in January, saying he took "full responsibility" for the tragedy.
Making public the previously classified finding on Thursday, Obama expressed his "deepest apologies" to the families of the two hostages, Warren Weinstein and Giovanni Lo Porto.
Two other Americans linked to al-Qaeda, including spokesman Adam Gadahn, were killed in operations at around the same time, the White House said.
"Based on information and intelligence we have obtained, we believe that a US counter-terrorism operation targeting an al-Qaeda compound in the Afghanistan-Pakistan border region accidentally killed Warren and Giovanni this past January," Obama said in an unscheduled statement.
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"As president and as commander-in-chief, I take full responsibility for all our counter-terrorism operations, including the one that inadvertently took the lives of Warren and Giovanni, he said.
"I profoundly regret what happened. On behalf of the United States government, I offer our deepest apologies to the families."
Weinstein was snatched after gunmen tricked their way into his home in Lahore on August 13, 2011 shortly before he was due to return home after seven years working in Pakistan.
He later appeared in a video in which, under apparent coercion, he asked the United States to free al-Qaeda prisoners.
Italian aid worker Lo Porto, 39, disappeared in January 2012 in Pakistan.
Weinstein's widow said in a statement that "we are devastated by this news and the knowledge that my husband will never safely return home."
The White House statement did not identify which US agency carried out the operation, which suggests it was carried out by an intelligence service rather than a military unit.
If confirmed, it would be the latest controversy to hit Obama's counter-terrorism operations, which - while killing Osama bin Laden - have relied heavily on secret drone strikes.
"We have concluded that Ahmed Faruq, an American who was an al-Qaeda leader, was killed in the same operation that resulted in the deaths of Dr. Weinstein and Mr. Lo Porto," the White House said.
"We have also concluded that Adam Gadahn, an American who became a prominent member of al-Qaeda, was killed in January, likely in a separate US government counterterrorism operation," it added.
"While both Faruq and Gadahn were al-Qaeda members, neither was specifically targeted, and we did not have information indicating their presence at the sites of these operations."
In his statement, Obama said the US believed that the operation resulting in the hostage deaths "did take out dangerous members of al-Qaeda."
