The deaths of Dr Warren Weinstein, a US government aid worker, and Giovanni Lo Porto, an Italian aid worker, who were being held captive in the Afghanistanand Pakistan border region, have placed unprecedented pressure on Barack Obama’s secret program of targeted drone killings.

They mark the first time a US drone strike has inadvertently killed innocent hostages, and have forced the Obama administration to disclose an unprecedented amount of information about what would typically be a highly classified operation.

Among the most startling admissions was the fact the drone strike was authorized by a senior counter-terrorism official without any specific information about who was in the immediate area, which had merely been identified as a compound frequented by al-Qaida leaders.

Hours after Obama personally expressed his “profound regret” over the deaths, and announced an immediate review of the operation, his press secretary, Josh Earnest, said the victims’ families would be compensated, and gave unprecedented details about the intelligence that led to the operation.

Earnest said the compound was targeted based on “near-certain” intelligence that indicated it was being frequented by at least one al-Qaida leader, and that no civilians were in the area. Earnest said the review may raise “legitimate questions” that would force the administration to change its protocols for such operations.

Conceding that the operation was not ordered against any individual targets, Earnest said the administration only discovered later that the compound was occupied by Weinstein, La Porto and another American named Ahmed Farouq, who the White House says was a “leader” of the terrorist group.

Farouq was not, however, the target of the operation. The drone strike was not targeted at known al-Qaida members; instead, it was directed against anyone in the vicinity of what the US believed was a compound being used by the terrorist group.

A second drone strike in January, which killed Adam Gadahn, another American who the US says had become an al-Qaida fighter, was also targeted at terrorist compound, without knowledge of who specifically was in the vicinity.

There was no specific authorisation to kill Farouq and Gadahn.

Earlier, Obama praised what he claimed was his administration’s exceptionally transparent response to the tragedy.

He did not mention the two American al-Qaida members in the statement from the White House, in which he sought to explain how his counter-terrorism strike could have take the lives of two hostages. Neither did he use the word “drone”.

“As president and as commander-in-chief, I take full responsibility of all of our counter-terrorism operations, including the one that inadvertently took the lives of Warren and Giovanni,” Obama said. “I profoundly regret what happened. On behalf of the United States government, I offer our deepest apologies to their families.”

Yet the president struck a surprisingly defiant tone, insisting that his administration had acted on the best intelligence available at the time and claiming that his decision to declassify the operation and initiate a review was a sign of American exceptionalism.

He said he had decided to make the existence of the operation public because Weinstein and Lo Porto’s families “deserve to know the truth” and “the United States is a democracy, committed to openness, in good times and in bad”.