An American and an Italian who had been held hostage for several years by al Qaeda in the border region of Pakistan and Afghanistan were inadvertently killed in a US counterterrorism operation in January, President Barack Obama said on Thursday.
Two Americans, both al Qaeda leaders, were also unintentionally killed around the same time; one of them in the same operation that claimed the lives of the hostages, the White House said.
The American hostage killed was Warren Weinstein, who had been held by the al Qaeda since 2011, and the Italian was Giovanni Lo Porto, who was taken in 2012. Both were aid workers.
The counter-terrorism operation, the White House said, had targeted an al Qaeda compound but "we had no reason to believe either hostage was present".
"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," President Barack Obama said at a news conference.
"As President and Commander-in-Chief, I take full responsibility for all counterterrorism operations, including the one that inadvertently took the lives of Warren and Giovani."
The killings are likely to raise questions once again about the drone programme that has been criticised both at home and abroad for causing civilian casualties; and for the extra-judicial nature of punishment meted out by it.
Weinstein (73) was abducted in Lahore in 2011, while working with a US consulting firm. Lo Porto (40), who was from Sicily, worked for a German organisation.
Weinstein's wife, Emily, said in a statement the family was devastated. "We were so hopeful that those in the US 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."
Al Qaeda had demanded the release of members of the organisation being held by the US, which has said it doesn't negotiate with hostage-takers.
The American al Qaeda leaders killed were Ahmed Farouq and Adam Gadahn. "Neither was specifically targeted, and we did not have information indicating their presence at the sites of these operations," the White House said.
Italy described the death of hostage Lo Porto a "tragic and fatal error by our US allies" but said "terrorists" were entirely to blame.
The foreign ministry said in a statement that Lo Porto had died "because of the tragic and fatal error by our American allies, recognised by President (Barack) Obama".
It added: "The responsibility for his and Warren Weinstein's death however... was entirely the terrorists against whom we confirm Italy's commitment alongside our allies."
With inputs from AFP