U.S. special operations forces searching for a pair of kidnapped American University of Kabul professors raided a compound last month and got into a gun battle that left a half-dozen militants dead, a senior defense official said Thursday.

But when the shooting was over, the captive educators — an American and an Australian — were not at the location in Jalalabad, the official said. And it was not clear if they had been held there at all.

Afghan security personnel keep watch near the site following the militants' raid that targeted the elite American University of Afghanistan, in Kabul on Aug. 25. WAKIL KOHSAR / AFP - Getty Images

The professors were abducted on Aug. 7 as they sat in their car after classes. They have not been named at the request of authorities and no group has claimed responsibility for the kidnappings. But the Haqqani network is suspected to be holding them, the official said.

Not long after the profs went missing, the U.S. military got wind of where they might be and sent the National Security staff at the White House a memo seeking authorization to act, the official said.

The NSA staff, however, had some reservations and kicked it back to the military to fill in the blanks. The official did not say what the hitch was.

But the military updated the request and 24 hours later it was approved, the official said. A short time later, SEAL Team 6 moved in and attacked the target. The exact date of the raid was not divulged.

With President Obama on vacation on Martha's Vineyard for from Aug. 7 to Aug. 23, the White House had granted the military blanket authority to pursue the kidnappers during that period, the official said.