Updated 11.48am: A US counter-terrorism operation in January killed two hostages.

They were an American contractor, Warren Weinstein, and Italian aid worker Giovanni Lo Porto.

The drone strike was on an al Qaeda compound in the border region of Afghanistan and Pakistan.

Both hostages had been in captivity for two years.

White House spokesman Josh Earnest says their near-certainty information about the presence of civilians was wrong in this case.

"There were hundreds of hours of surveillance, against that particular compound, and this surveillance included near continuous surveillance in the days leading up to the operation."

President Barack Obama has given his justification for the drone strike.

"We believed that this was an al-Qaeda compound, that no civilians was present, and that capturing these terrorists was not possible. We believe that the operation did take out dangerous members of al-Qaeda."

Obama has apologised to the men's families, and spoken to the Italian Prime Minister.

"I profoundly regret what happened."

But wife Elaine Weinstein says she and her family are disappointed with the US and Pakistani governments' efforts to secure her husband's release from his Al-Qaeda captors.

She says there are no words to do justice to the disappointment and heartbreak they're going through.

They're looking forward to the results of a US government investigation into the incident.

 

The US will compensate the victims' families.