U.S Special Operations Forces launched a rescue mission to retrieve two men kidnapped by insurgents in Afghanistan last month, but the hostages were not there when the rescue team arrived, U.S. defense officials say.

Pentagon press secretary Peter Cook said the rescue mission was approved by Defense Secretary Ash Carter and authorized by President Barack Obama.

Cook said no U.S. personnel or civilians were injured. He declined to provide more details, citing the need "to protect the safety of hostages and operational security."

According to defense officials, the mission was delayed one day because of questions about whether the hostages, an American and an Australian who worked at the American University of Afghanistan, were there. 

When U.S. commandos arrived at the house where they believed the hostages were held, they killed seven enemy fighters, the officials said.

The two men were kidnapped from their vehicle as they traveled from the university to their residence in Kabul on August 7. The rescue was attempted not long after their kidnapping.

The rescue attempt occurred before militants stormed American University on August 24 in an attack that left 16 people dead.

Based on reporting by AP, AFP, and Reuters