US President Barack Obama today (23 April) apologised for a counterterrorism operation in January that accidentally killed two aid workers held hostage by al-Qaeda, American Warren Weinstein and Italian Giovanni Lo Porto.

"As a husband and as a father, I cannot begin to imagine the anguish that the Weinstein and Lo Porto families are enduring today," Obama told reporters, with a deep sigh, saying he took responsibility for the deaths and has ordered a full review.

"I profoundly regret what happened," Obama said, explaining he declassified some of the details of the operation so that the families could know what happened.

Obama says US officials believed the target was an al-Qaeda compound without civilians.

"We believed that this was an al-Qaeda compound, that no civilians were present and that capturing these terrorists was not possible. And we do believe that the operation did take out dangerous members of al-Qaeda. What we did not know, tragically, is that al-Qaeda was hiding the presence of Warren and Giovanni in this same compound."

Obama says has ordered details of the January operation to be declassified in an effort to disclose the truth to the families and be transparent to the American people.

"I directed that the existence of this operation be declassified and disclosed publicly. I did so because the Weinstein and Lo Porto families deserve to know the truth. And I did so because, even as certain aspects of our national-security efforts have to remain secret in order to succeed, the United States is a democracy committed to openness in good times and in bad," Obama said.