The White House said Thursday that American Warren Weinstein and Italian national Giovanni Lo Porto were killed in a January attack on an al Qaeda compound.
"No words can fully express our regret over this terrible tragedy," the White House said, revealing the previously classified finding in a written statement shortly before US President Barack Obama held a press conference.
"Warren and Giovanni were aid workers in Pakistan devoted to improving the lives of the Pakistani people," Obama said, adding, "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 that the mission was "fully consistent" with guidelines for conducting counterterrorism missions in the region and that there had been no information to show that the two hostages were being held in the targeted compound.
According to the White House, Weinstein had been held by al Qaeda since 2011 and Lo Porto since 2012. An American al Qaeda member, Ahmed Farouq, was killed in the same operation. Adam Gadahn, another prominent al Qaeda member and US citizen, was also killed in a separate January operation, the White House said.
Obama said he had already directed a full review of what happened.
"We will identify the lessons that can be learned from this tragedy," he said, leaving the press conference without taking questions.
se/rc (Reuters, AFP, AP, dpa)