The White House announced Thursday that two hostages held by al Qaeda were accidentally killed during a counterterrorism operation in January.

Warren Weinstein, an American USAID contract worker held since 2011, and Giovanni Lo Porto, an Italian kidnapped in 2012, were killed in counterterrorism operations carried out by the U.S government.

"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," President Barack Obama said Thursday, according to CNN.

Officials told the station a U.S. military drone strike killed the hostages.

"The operation targeted an al Qaeda-associated compound, where we had no reason to believe either hostage was present, located in the border region of Afghanistan and Pakistan," the White House said in a Thursday statement, according to The New York Times.

"No words can fully express our regret over this tragedy."

The White House also announced that two American members of al Qaeda, Ahmed Farouq and Adam Gadahn, were also unintentionally killed in counterterrorism missions in the same region.

Weinstein, 73, was providing aid to Pakistani families when he was kidnapped in August 2011. Over the years al Qaeda released videos of the captive, including one in late 2013 of Weinstein pleading with the U.S. and Obama to rescue him.

At the time his wife Elaine told ABC News she "wanted to die right there on the spot" when she saw the video. "He has no idea how hard we've tried to get him back....and it's just heartbreaking because he's asking for help and I can't give him any."