A suicide bomber who killed seven CIA officials at an outpost in Afghanistan earlier this week was on the premises because he had been invited, according to media reports.

The man, who was dressed as a member of the Afghan National Army, entered the camp because he was being "courted as an informant" for intelligence-gathering purposes, the Associated Press first reported Thursday afternoon.

He was not searched before entering the outpost in the Khost province of Afghanistan, senior intelligence officials also told the AP.

Earlier in the day, President Barack Obama offered his sympathies for the fallen agents and praised the entire intelligence agency for its dangerous yet important work.

"These brave Americans were part of a long line of patriots who have made great sacrifices for their fellow citizens, and for our way of life," the president wrote. "The United States would not be able to maintain the freedom and security that we cherish without decades of service from the dedicated men and women of the CIA."

Nevertheless, the news is likely to frustrate further those who are already fuming at an unrelated, attempted bombing aboard an international flight that landed in Detroit last week.